- Melt butter in a heavy saucepan.
- Add onion and stir over moderate heat until onion is transparent.
- Add mushrooms and cook another 4-5 minutes, stirring.
- Remove from heat and stir in flour and meat concentrate.
- Slowly add stock, stirring continuously. Add bay leaf and pepper.
- Bring to a boil, reduce heat and simmer 5-10 minutes.
- Remove bay leaf and stir in the cream.
- Garnish with croutons.