Preheat the oven to 160°Ⅽ

For the pasta:

Place the lasagne sheet in a deep bowl and add water just to cover them. Let the pasta absorb the water until they soften.

For the ragu:

Heat a large pan and add the olive oil to cook the mince until browned all over. Remove then mince from the pan and place in a separate plate.

Add to the pan the celery, onion and garlic and cook until softened. Return the meat to the mixture, adding the flour and stir well. Add the stock and let the mixture boil.

Then insert the sugar, tomato puree and thyme and stir again. Finally, add the canned tomatoes and bring again the mixture to the boil.

For the sauce:

Melt the butter in a pan. Add the flour and cook over the heat, while gradually adding the hot milk. Whisk until the sauce thickens and add the mustard and parmesan. Finally season well with salt and pepper.

For the Lasagne:

Place the 4 Lasagne sheets at the bottom of your pan. Add a third of the ragu and a third of the white sauce. Then add another layer of Lasagne and add half of the ragu and white sauce of what is left. Then add the last layer of pasta and the rest of the ragu and sauce. Finish with spreading the cheddar all over the surface.

Add the dish to the oven for around 45 minutes and let cook until the top is golden brown, and there are bubbles around the edges.