Sautee the mushrooms chopped very finely and reserve

Sautee the leeks and add chopped tomatoes and mushrooms to pan

Cook together for about 20 minutes adding a spoonful of sugar to counteract tomatoes acidity. Season to taste with salt and pepper

While veg cook start the bechamel sauce. Melt butter in frying pan and add as much flour as it absorbs to make a smooth paste that doesn't stick to the pan. Add milk slowly incorporating to the paste until a thick sauce develops, you can make is as thin as you like it by adding extra milk

Once the sauce is ready reserve

Cook in a preheated oven at 180°C. Serve with extra vegetables or salad. I like my lasagna with pickled green beans.