Bechamel

• Melt butter in a medium saucepan over medium-low.
• Whisk in flour until mixture forms a paste, about 2 minutes.
• Gradually whisk in milk.
• Increase heat to medium. Cook, stirring constantly and scraping the bottom of the pot, until sauce thickens, 7 to 8 minutes.
• Stir in salt and nutmeg.

Bolognese meat sauce

• Melt butter in a large heavy pot over medium.
• Add onion, carrot and celery. Cook, stirring occasionally, until soft, 5 to 7 minutes.
• Increase heat to medium-high. Add beef, garlic and salt. Cook, stirring to break up meat, until no pink remains, 3 to 4 minutes.
• Add milk and cook until almost all liquid has evaporated, 7 to 8 minutes.
• Add wine and cook until almost all liquid has evaporated, 6 to 7 minutes.
• Stir in passata. Boil, then reduce heat to low and simmer, stirring occasionally, until slightly thickened, 45 minutes.

To assemble

• Spread 1/2 cup béchamel in the bottom of a 9 × 13-inch baking dish.
• Top with 3 noodles. Spread 1 1/2 cups Bolognese meat sauce evenly over noodles. Drizzle with 1/2 cup béchamel.
• Top with 3 more noodles. Spread ricotta evenly over noodles. Season with fresh pepper. Spread another 1 1/2 cups meat sauce evenly over ricotta. Drizzle with 1/2 cup béchamel.
• Top with remaining 3 noodles. Spread remaining 1 1/2 cups meat sauce evenly over noodles. Drizzle with remaining 1/2 cup béchamel.
• Sprinkle evenly with mozzarella.
• Cover pan with foil and bake in centre of oven, 45 minutes.
• Remove foil, then sprinkle with parmesan.
• Bake until golden and bubbly, about 10 more minutes.
• Let lasagna stand 10 minutes before serving.