Melt butter in large, heavy pan. Add mushrooms and cook over medium heat about 4 minutes. Remove mixture from heat and blend in flour. Return pan to heat and add stock slowly, stirring constantly. Add salt, pepper, garlic powder and brown sugar. Bring mixture to a boil, reduce heat and simmer about 5 minutes. Remove from heat and stir in cream. Serve immediately. Makes 6 side-dish servings.