Preheat oven to 350°F. Wash the mushrooms and remove the stems. Pat the mushroom caps dry with a paper towel. Chop mushroom stems very fine and combine with next seven ingredients. Spoon the mixture into the mushroom caps and place in a shallow baking dish. Dot each with butter. Bake for 20-25 minutes. Remove from the oven, sprinkle with chopped parsley and serve immediately.
Prepare and refrigerate ahead of time. When you are ready to serve, pop in a preheated oven. You may need to extend the cooking time a few minutes if dish is coming right out of the refrigerator.