Clean the celery and carrot and chop finely. Peel and finely chop the onion. If using, wash the tomatoes and cut them in half. Cut the lamb into small cubes.

Heat the olive oil in a frying pan or iron skillet and add the chopped vegetables. Once they start to soften slightly, add the lamb pieces.

Season with salt and pepper and cook over medium heat for about 10 minutes.

When the lamb is almost cooked but still pink, add the rosemary and wine and let the alcohol evaporate. Add the halved cherry tomatoes (if using) and cook until they start to soften.

Finally add two thirds of the tomato passata and the cup of stock and cook over a medium heat for about 20 minutes, until the sauce thickens. If you think it’s too thick add more passata or stock until you have the consistency you want.

While the ragu is cooking make the béchamel sauce. In a saucepan, let the butter melt over a moderate flame. Add the flour a little at a time, stir carefully until you have a paste. Make sure any lumps of flour dissolve.

Then pour in the milk a little at a time, continuing to stir until it starts to thicken. Add salt, nutmeg and grated cheese, if you are using it. Continuing stirring until the cheese melts and the béchamel is thick enough. If it gets too thick you can add more milk.

Put a pot of water onto to boil for the pasta if you are using dried lasagne sheets. Add salt once it starts to boil and bring to the boil again. Cook the pasta sheets for only half the recommended cooking time. You may want to add a little oil to the water to stop them sticking together. It's best to cook them a few at a time. Drain the pasta and lay the sheets on a tea towel until ready to assemble your lasagna.

Once everything is ready assemble your lamb lasagna. Start with a layer of ragu. Then make a layer of pasta, with ragu and béchamel on top. Then another layer of pasta, ragu and béchamel.

Continue until the dish is almost full and finish off with a layer of pasta with only béchamel on top sprinkled with pecorino or Parmigiano.

Bake the lamb lasagna for at least 30 minutes at 180-200 ° until the top is golden and slightly crispy. Let the lasagna stand for 10 minutes before cutting and serving.