01 -
Melt unsalted butter in a large skillet over medium heat. Add all-purpose flour and whisk continuously, cooking for about 6 minutes until the mixture turns golden.
02 -
Warm whole milk in a saucepan until nearly boiling. Gradually pour in the milk, one cup at a time, into the butter-flour roux, whisking thoroughly after each addition to achieve a smooth consistency.
03 -
Bring the sauce to a gentle boil, then reduce heat and simmer for 10 minutes, stirring constantly. Season with fine salt, freshly ground black pepper, and ground nutmeg.
04 -
Preheat the oven to 400°F. Slice the parboiled Russet potatoes and arrange them to line the bottom and sides of a round casserole dish.
05 -
Combine ground beef, diced onion, dried parsley, dried paprika, a pinch of fine salt, black pepper, and a small amount of nutmeg in a bowl. Mix thoroughly and shape the mixture into evenly sized meatballs.
06 -
Arrange the meatballs on top of the potato layer. Place additional potato slices between each meatball as desired.
07 -
Pour the prepared béchamel sauce evenly over the meatballs and potatoes. Sprinkle shredded mozzarella cheese generously across the top.
08 -
Bake the casserole in the preheated oven for 15 minutes, or until the cheese is fully melted and develops a golden brown color.