Sauté the Meat Filling
Brown: Sauté ground beef in a skillet until browned. Add onion, carrot, and garlic; cook until softened.
Simmer: Stir in tomato puree and spices. Let simmer for 5 minutes until thickened, then remove from heat.
Craft the White Binder Sauce
Roux: Melt butter in a pot and whisk in flour for 1 minute.
Thicken: Gradually pour in milk, whisking constantly over medium heat until the sauce thickens and coats a spoon.
Season: Stir in salt, pepper, and nutmeg.
Temper and Emulsify
Cheese: Remove sauce from heat and stir in the mozzarella until melted.
Eggs: Whisk the whole egg and egg yolk together, then slowly stir them into the warm sauce to create the structural binder.
Coat the Spaghetti
Combine: Place cooked spaghetti in a large bowl. Pour 2/3 of the white sauce over the pasta and toss until every strand is coated.
Layer and Assemble
Base: Press the saucy spaghetti into a greased 9x13 inch baking dish.
Middle: Spread the meat filling evenly over the pasta.
Top: Pour the remaining white sauce over the meat and sprinkle generously with extra mozzarella.
The Bake
Cook: Bake at 400°F (200°C) for 20–25 minutes until the cheese is bubbly and golden brown.
Set: Allow the dish to cool completely before slicing to ensure the portions hold their shape.