Clean the leek, cut in half lengthways and cut into fine strips. Peel the tomatoes, chop them roughly, peel and finely chop the carrots.
Heat 1 tablespoon of butter in a pan and fry the cut vegetables in it. Add the lentils with a bay leaf and fry them too. Pour in the vegetable stock and simmer for 15 minutes. Season the lentil vegetables with 100 g crème fraîche, vinegar, salt, pepper and chilli.
Grease a baking dish, pour in some lentil vegetables and place lasagne sheets on top. Then repeat the process until the ingredients are used up.
Mix 100 g of crème fraîche with 2 tablespoons of butter and grated cheese and place on top of the lasagna. Bake the lentil lasagne on the middle rack in the oven at 180 ° C for 30 minutes until golden brown.