Step 1: Prepare the Potatoes

• Peel the potatoes and cut them into thin slices. Boil the sliced potatoes in salted water for about 10-12 minutes, or until they are slightly tender but not fully cooked. Drain and set aside.

Step 2: Sauté the Vegetables

• In a large frying pan, melt 30 grams of butter over medium heat. Add the chopped onion and garlic, and sauté for about 3-4 minutes until softened and fragrant.
• Add the grated carrot and chopped red bell pepper to the pan and continue sautéing for another 5 minutes. Once the vegetables are tender, set them aside.

Step 3: Make the Creamy Sauce

• In a saucepan, melt the remaining 30 grams of butter over medium heat. Stir in the flour to create a roux, and cook for about 2 minutes, stirring continuously to avoid lumps.
• Slowly pour in the milk, whisking constantly until the sauce begins to thicken (about 4-5 minutes).
• Stir in the mayonnaise, season with salt and pepper to taste, and set the sauce aside.

Step 4: Assemble the Casserole

• Preheat your oven to 180°C (350°F).
• In a large ovenproof dish, layer the boiled potato slices at the bottom. Add the sautéed vegetable mixture on top of the potatoes, followed by the sliced sausages.
• Crack the eggs directly over the dish, making sure to space them evenly. Sprinkle the grated mozzarella cheese over the entire dish.
• Pour the creamy sauce over the layers, making sure it spreads evenly across the top.

Step 5: Bake the Casserole

• Bake the casserole in the preheated oven for about 25-30 minutes, or until the eggs are fully cooked and the cheese is golden and bubbly.

Step 6: Garnish and Serve

• Once out of the oven, let the casserole rest for 5 minutes. Garnish with chopped green onions and serve it warm with a side salad or some fresh bread.