Make the meat filling

• Heat the olive oil in a frying pan over medium heat.
• Add the chopped onion and cook until soft and translucent.
• Add the minced garlic and cook for 1 minute until fragrant.
• Add the ground beef and brown it, breaking it up with a spoon.
• Pour in the tomato passata, season with salt, pepper and oregano and let it simmer until thickened.

Make the béchamel

• Melt the butter in a saucepan over low heat.
• Whisk in the flour and cook for 1 minute to make a roux.
• Gradually pour in the milk while whisking constantly to avoid lumps.
• Season with salt, pepper and grated nutmeg and cook until the sauce thickens.

Fill the cannelloni

• Spread a layer of béchamel and tomato sauce on the bottom of the baking dish.
• Fill the cannelloni tubes with the meat filling (or roll the filling in the pasta sheets).
• Arrange the filled cannelloni side by side in the dish.

Assemble and bake

• Cover the cannelloni with the remaining tomato sauce and béchamel.
• Sprinkle the grated mozzarella and parmesan over the top.
• Bake in a preheated oven at 180 °C until golden and bubbling.

Rest and serve

• Let the cannelloni rest for a few minutes before serving.
• Serve hot, cut into portions.