Clean fish and pat dry with paper towels. In skillet melt 3 tbsp. butter, saute mushrooms until tender. Add garlic, salt, pepper to taste and 2 tbsp. cream. Simmer GENTLY 2 or 3 minutes.
Arrange trout in a buttered baking dish. SPoon mushroom mixture over them. Cover and bake at 375 degrees F 15 to 20 minutes or until fish flakes to the touch of a fork.
In a saucepan melt 1 tbsp. butter, whisk in flour, add remaining cream and whisk until smooth and thickened.
Remove cooked trout from oven. Drain liquid and stir into cream sauce. Pour sauce over fish. Garnish with parsley.