Prepare the Ingredients: Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish.

Thinly slice the russet potatoes, aiming for even slices so they cook uniformly.

Cook the Ground Beef Mixture: In a skillet over medium heat, add the ground beef, chopped onion, and minced garlic. Cook until the beef is browned and the onions are soft, about 5-7 minutes. Drain any excess fat.

Season the mixture with salt, black pepper, and paprika if using. Set the cooked beef mixture aside.

Make the Cheese Sauce: In a medium saucepan, melt the butter over medium heat. Stir in the flour, whisking constantly for about 1 minute to create a roux.

Slowly add the milk and heavy cream, continuing to whisk until the mixture thickens, about 5 minutes.

Add 1 1/2 cups of shredded cheddar cheese to the sauce and stir until the cheese is fully melted and the sauce is smooth. Season with a bit of salt and pepper to taste.

Assemble the Casserole: In the prepared baking dish, arrange a layer of sliced potatoes, slightly overlapping them. Sprinkle some of the ground beef mixture over the potatoes and then pour a portion of the cheese sauce on top.

Repeat these layers until all the ingredients are used, ending with a layer of cheese sauce. Add additional shredded cheddar cheese on top for an extra cheesy crust.

Bake the Casserole: Cover the baking dish with aluminum foil and bake for 40 minutes.

Remove the foil and bake for an additional 15-20 minutes, or until the top is golden and bubbly and the potatoes are fork-tender.

Garnish and Serve: Once out of the oven, let the casserole sit for a few minutes to set. Garnish with chopped green onions or parsley for a touch of color and flavor.

Serve hot and enjoy the melty, cheesy layers of goodness.