Make the Bolognese

• Heat the olive oil in a frying pan and soften the onion, carrot, celery and garlic.
• Add the ground beef and brown it well, breaking it up as it cooks.
• Pour in the tomato puree, season with salt and pepper and simmer until thick and rich.

Make the bechamel

• Melt the butter in a saucepan, add the flour and cook briefly into a roux.
• Pour in the milk gradually, whisking constantly until smooth and creamy.
• Season with salt, pepper and nutmeg and let it thicken slightly.

Cook the lasagna sheets

• Boil the lasagna sheets in salted water until al dente.
• Drain and lay them flat on a clean surface.

Fill and roll

• Spread Bolognese and bechamel over each sheet and sprinkle with Parmesan.
• Roll each sheet up tightly into a spiral.

Assemble the dish

• Spread a layer of bechamel and Bolognese in the baking dish.
• Stand the rolls upright, close together, in the dish.
• Spoon over more bechamel and Bolognese and top with mozzarella and Parmesan.

Bake

• Bake until golden and bubbling.
• Let it rest briefly before serving.