01 - Preheat oven to 350°F.
02 - Heat olive oil in a large skillet over medium heat. Add onion and cook until translucent, about 5 minutes. Add garlic and cook for 1 minute.
03 - Add ground beef to the skillet. Cook, breaking it up with a spoon, until browned throughout.
04 - Stir in crushed tomatoes, tomato paste, oregano, basil, salt, pepper, sugar, and water. Simmer uncovered for 20–25 minutes, stirring occasionally, until sauce thickens.
05 - Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1–2 minutes without browning.
06 - Gradually add warmed milk while whisking constantly to prevent lumps. Cook, stirring continuously, until sauce thickens, about 5–7 minutes. Stir in nutmeg, salt, and white pepper. Remove from heat.
07 - Cook lasagna noodles according to package directions if not using no-boil variety. Drain well and set aside.
08 - Spread a thin layer of meat sauce in the bottom of a 9x13 inch baking dish. Arrange a layer of noodles over the sauce.
09 - Top noodles with ⅓ of the meat sauce, ⅓ of the béchamel sauce, and sprinkle with mozzarella and Parmesan. Repeat layering twice more, finishing with remaining béchamel and cheese on top.
10 - Cover baking dish with foil. Bake for 30 minutes.
11 - Remove foil and bake an additional 15–20 minutes until cheese is golden and sauce is bubbling around edges.
12 - Let lasagna stand for 15 minutes before slicing and serving to allow layers to set.