I am making this recipe of my sister's today:

• sauté one large onion and  100 g of minced beef in a little oil,
• put in 400 g of cut-up leeks with vegetable broth, bring to boil, and leave to simmer for about 20 minutes
• then add 2 pieces of processed cheese and let it melt,
• clean and dice  175 g of fresh mushrooms, add to the soup, and allow to simmer for a while longer

Serve with some darkish bread.