The MOST DELICIOUS Spinach Lasagna . Very Easy and Very Fast!

Ingredients:
Lasagne sheets
Mushrooms 800 g
Spinach 100 g
Onion 2 pieces
Salt and seasonings
Basil 10 g
Butter 50 g
Flour 2 tablespoons
Milk 300 ml
Cheese 200 g

Bake for 20-25 minutes at 200 degrees.