Creamy casseroles are the culinary equivalent of a cozy knit blanket, and this Broccoli-Potato Mushroom Au Gratin is no exception. Tender florets of emerald broccoli, buttery chunks of potato, and sautéed mushrooms nestle under a velvety béchamel enriched with melting cheese and a whisper of nutmeg. The vegetables keep the dish bright and wholesome, while the golden crust and luxurious sauce deliver pure comfort-food satisfaction. Whether you serve it as a vegetarian main, a holiday side, or make-ahead meal-prep hero, this bake promises to win over picky kids, hungry teens, and sophisticated palates alike.
Cooking Time
Prep Time: 25 minutes
Par-Cooking & Sauce: 15 minutes
Bake Time: 35 minutes
Total Time: about 1 hour 15 minutes
Yield: 6 generous servings
Ingredients
Vegetables
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1 medium head broccoli, cut into bite-size florets (≈ 300 g / 10.5 oz)
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500 g / 17.6 oz waxy or all-purpose potatoes, scrubbed and cut into 2 cm cubes
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Water for boiling, plus 1 Tbsp salt
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1 bay leaf
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4–5 whole peppercorns
Mushroom Sauté
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2 Tbsp olive oil, divided
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1 small red onion, thinly sliced
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4 white mushrooms (≈ 150 g), sliced
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Pinch salt and freshly ground black pepper
Nutmeg Cheese Sauce (Mornay)
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2 Tbsp unsalted butter
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2 Tbsp all-purpose flour
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500 ml / 2 cups whole milk, room temperature
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½ tsp freshly grated nutmeg
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½ tsp fine salt (plus more to taste)
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¼ tsp freshly ground black pepper
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120 g / 1 heaping cup shredded semi-hard cheese (Gouda, cheddar, or Gruyère)
Assembly & Finish
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1 Tbsp olive oil, for greasing dish
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Additional 60 g / ½ cup shredded cheese for topping
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Optional: 2 Tbsp panko breadcrumbs for extra crunch
Step-by-Step Cooking Directions
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Blanch the Broccoli
Fill a medium pot with water, add a generous pinch of salt, and bring to a rolling boil. Drop in broccoli florets; blanch for just 2–3 minutes until bright green and crisp-tender. Drain immediately and rinse under cold water to stop cooking. -
Par-Boil the Potatoes
In the same pot, add fresh water, 1 Tbsp salt, bay leaf, and peppercorns. Bring to a boil, slide in potato cubes, and simmer 8–10 minutes until fork-tender but not falling apart. Drain, discard bay leaf and peppercorns, and spread potatoes on a tray to steam-dry. -
Sauté the Aromatics
Heat 1 Tbsp olive oil in a skillet over medium. Add red onion; cook 2–3 minutes until translucent. Push onion to the side, drizzle remaining oil, add sliced mushrooms, season lightly, and sauté 5–7 minutes until golden and their liquid evaporates. Remove from heat. -
Whisk the Nutmeg Cheese Sauce
In a heavy saucepan melt butter over low-medium heat. Sprinkle in flour, whisking constantly for 1 minute to form a pale roux. Gradually pour in milk, whisking vigorously to avoid lumps. Raise heat to medium; cook, stirring, until the sauce thickens enough to coat a spoon (about 4 minutes). Season with nutmeg, salt, and pepper. Off heat, stir in 120 g shredded cheese until glossy. -
Assemble the Au Gratin
Preheat oven to 180 °C / 350 °F. Grease a 22 × 30 cm (9 × 13 in) baking dish with olive oil. Spoon a thin veil of cheese sauce over the base to prevent sticking. Layer half the potatoes, half the broccoli, and half the mushroom–onion mixture. Drizzle with one-third of the sauce. Repeat layers, finishing with remaining sauce. Sprinkle the top with reserved cheese and (if desired) panko for crunch. -
Bake to Bubbling Perfection
Slide the dish onto the middle rack and bake 35 minutes, until the top is deeply golden, the edges are bubbling, and the vegetables yield to a knife. Let stand 5 minutes before serving so the sauce sets slightly.
Nutritional Information (per serving; 1/6 recipe)
Calories 385 | Protein 14 g | Carbohydrate 34 g | Fiber 5 g | Total Fat 22 g (Sat 11 g) | Sodium 640 mg | Calcium 270 mg
Values are estimates based on standard ingredient data.
Origins and Popularity of the Recipe
Gratin dishes originated in French home kitchens, where béchamel or cream was poured over sliced potatoes and baked until a browned “gratin” (from gratter, to scrape) formed on top. Over time, cooks worldwide customized the template, adding seasonal vegetables, cheeses, and even proteins. In the American Midwest, broccoli-cheddar casseroles became potluck royalty, while British pubs embraced cauliflower cheese. This recipe unites classic French technique with the vegetable-forward sensibility of modern comfort cooking—no wonder it appears on brunch menus, holiday tables, and weeknight meal-prep lists across continents.
Reasons Why You’ll Love the Recipe
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One-Pan Convenience: Main carbohydrate, veggie, and sauce bake together—fewer dishes.
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Kid-Friendly: The creamy cheese cloak tames broccoli skeptics.
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Meal-Prep Star: Reheats beautifully; flavors meld overnight.
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Seasonal Flexibility: Swap in asparagus in spring or butternut squash in autumn.
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Make-Ahead Magic: Assemble 24 hours early, refrigerate, and bake when needed.
Health Benefits
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Broccoli’s Brassica Power: Rich in sulforaphane, vitamins C, K, and folate, supporting immune and bone health.
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Potato Potassium: Helps regulate blood pressure and provides steady energy.
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Mushroom Umami: Supplies selenium, B-vitamins, and plant-based vitamin D.
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Milk & Cheese Calcium: Promotes strong bones and gives satiating protein.
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Olive Oil Antioxidants: Adds heart-healthy monounsaturated fats.
Serving Suggestions
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Brunch Board: Plate squares beside mixed-green salad, crusty baguette, and mimosas.
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Weeknight Pairing: Serve with roasted salmon or grilled tofu for protein boost.
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Holiday Spread: Nestle between roast turkey and cranberry sauce as a vegetarian star.
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Soup & Gratin Duo: Ladle tomato-basil soup alongside for a cozy supper.
Common Mistakes to Avoid
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Watery Sauce: Pat vegetables dry and cook mushrooms until liquid evaporates.
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Lumpy Béchamel: Add milk gradually while whisking; room-temperature milk helps.
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Undercooked Center: Use shallow dish and check that knife pierces through bubbling sauce.
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Over-Salting: Cheese contributes sodium—season sauce lightly and taste.
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Rubbery Top: Remove bake once golden; prolonged heat hardens cheese.
Pairing Recommendations
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Wine: A lightly oaked Chardonnay or floral Viognier mirrors the creamy, nutmeg notes.
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Beer: Belgian witbier’s citrus lifts the richness.
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Non-Alcoholic: Sparkling apple cider or iced herbal tea with lemon.
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Condiments: Dab of Dijon or spoon of zesty salsa verde balances the dairy.
Cooking Tips
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Chill shaped leftovers, then pan-fry wedges in butter for next-day crispy edges.
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Add 1 tsp Dijon to the sauce for subtle tang.
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Grate cheese yourself—pre-shredded varieties contain anti-caking agents that hinder melt.
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For deeper nutmeg flavor, grate whole nutmeg just before using.
Similar Recipes to Try
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Cauliflower–Leek Gratin with Gruyère Crust
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Sweet-Potato Spinach Lasagna Roll-Ups
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Cheddar Broccoli Twice-Baked Potatoes
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Mushroom & Swiss Quiche with Thyme Pastry
Variations to Try
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Gluten-Free: Replace flour with rice flour and top with crushed gluten-free crackers.
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Vegan Gratitude: Swap butter for plant margarine, milk for oat milk, and cheese for vegan shreds; thicken sauce with 1 Tbsp nutritional yeast.
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Protein Boost: Fold in shredded rotisserie chicken or cooked lentils between layers.
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Spicy Kick: Stir ¼ tsp cayenne into the sauce and top with pepper-jack cheese.
Ingredient Spotlight
Nutmeg: This warm, sweet spice from the seed of Myristica fragrans adds cozy depth to dairy-based sauces. A little goes a long way—½ teaspoon perfumes the entire dish without overpowering the vegetables, evoking memories of winter holidays and classic French Mornay sauce.
Conclusion
From its bubbling cheesy top to the last forkful of tender vegetables, this Broccoli-Potato Mushroom Au Gratin proves that everyday ingredients can transform into spectacular comfort food. The dish marries French technique with weeknight practicality, delivering a casserole that feels both nostalgic and fresh. Serve it once, and you’ll soon find yourself making double batches—one for tonight, and one tucked into the freezer for the next time you crave a creamy, veggie-packed hug on a plate.
Frequently Asked Questions
1. Can I assemble the gratin ahead and freeze it?
Yes—assemble, cool, wrap tightly, and freeze unbaked up to 2 months. Bake from frozen at 175 °C for about 60 minutes, shielding top with foil for first half.
2. Which cheese melts best in this recipe?
Gruyère melts smoothly and adds nutty complexity; cheddar offers punchy flavor; Gouda gives mild creaminess.
3. My sauce separated—what went wrong?
Boiling the béchamel aggressively can cause fat to split. Keep heat moderate and whisk constantly; adding cheese off heat also helps.
4. Can I use frozen broccoli?
Absolutely. Thaw, pat dry, and skip blanching; excess moisture may slightly thin the sauce, so reduce milk by 2 Tbsp.
5. How do I lower the fat content?
Use 1% milk and cut cheese to 90 g inside the sauce; omit butter and make a slurry of 2 Tbsp cornstarch + cold milk instead of roux.
6. Could sweet potatoes replace white potatoes?
Yes—dice them the same size, but par-boil only 5 minutes; their natural sugars brown quickly.
7. What herbs pair well here?
Fresh thyme or rosemary in the mushroom sauté adds fragrant depth; sprinkle chopped chives over the baked gratin.
8. Is nutmeg essential?
Nutmeg lends classic Mornay warmth, but you can substitute a pinch of white pepper and dried mustard for complexity.
9. Can I cook this in individual ramekins?
Divide layers among six 10-oz oven-safe dishes; bake 25–28 minutes until tops are golden.
10. How long will leftovers keep?
Refrigerate in an airtight container up to 4 days. Reheat portions at 180 °C for 12 minutes or microwave, then broil briefly to re-crisp the top.