1. Melt half the butter in a pan, sprinkle flour, stir well until smooth.
2. Slowly stir in milk or milk and stock. Bring to a boil, cook over low heat until it thickens.
3. Heat remaining butter in a fry pan, fry the onions until transparent and light golden. Add the seasonings and stir.
4. Add onion mixture to the soup. Mix well.
5. Stir in grated cheese. Stir well, cook for 5 minutes more and serve hot garnished with mint.