Lasagna, super delicious recipe

Ingredients
10 lasagna sheets
1 large onion(s), diced
220 g mushrooms, cut into thin leaves
120 g Emmental cheese, grated
350 g minced beef or lamb
420 g tomatoes, peeled, canned or fresh
220 ml cream or milk
1 tsp, heaped oregano
salt and pepper
1 tbsp butter
Garlic
preparation