1. In a heavy saucepan, melt butter over medium high heat.
2. Sauté onions and mushrooms 3-4 minutes, or until softened.
3. Add stock, barley, salt and pepper to taste. Bring to a boil. Reduce heat to low and simmer for 30 minutes.
4. Combine milk and flour in a jar with a tight fitting lid and shake until blended.
5. Stir milk and flour mixture into barley mixture and simmer 15 minutes until slightly thickened
