Lasagne al Forno

First, make the ragù. Heat the olive oil in a large pot over a medium heat. Add the onion, carrots and celery and cook gently for 10 minutes until soft. Increase the heat, add the beef mince and cook until browned all over.

Stir in the chopped tomatoes, tomato purée and oregano. Season well with salt and pepper. Bring to a simmer, then reduce the heat, cover and cook for at least 1 hour, stirring occasionally, until the sauce is rich and thick.

While the ragù simmers, make the béchamel sauce. Melt the butter in a saucepan, stir in the flour and cook for 1 minute to make a roux. Gradually whisk in the milk a little at a time until you have a smooth sauce. Bring to a gentle simmer, stirring constantly, until the sauce has thickened. Remove from the heat and stir in the grated Parmesan. Season with salt, pepper, and a pinch of nutmeg.

Preheat your oven to 180°C (350°F, Gas Mark 4).

To assemble, spoon a thin layer of ragù into the bottom of a 20x30cm baking dish. Cover with a single layer of lasagne sheets, followed by a layer of béchamel. Repeat the layers until you've used all the ingredients, finishing with a final layer of béchamel on top.

Sprinkle the grated mozzarella over the top.

Bake for 35-40 minutes, or until the top is golden brown and the sauce is bubbling at the edges.

Let the lasagne rest for at least 10 minutes before cutting and serving. This helps it hold its shape.