Finely chop the onion and sauté in a large saucepan with a little fat. Add the minced meat and fry well.
In the meantime, wash the leek and cut into half rings, then add to the minced meat and add the stock. Let the whole simmer until the leek is soft. Season properly with salt and pepper, stir in the cheese and add the mushrooms.
I always serve baguette (sometimes herb butter baguette) with it.