Wash mushrooms well.
Remove stems (save them for a casserole dish) and trim under edges of mushroom caps so they will hold plenty of filling.
Combine cheese, butter and garlic.
Set mushroom caps (top side down) on broiler pan or shallow baking pan and spoon cheese mixture into them.
Put low under broiler (middle of oven) and broil until cheese browns lightly and is bubbling well, about 3 minutes.
Note: Mushrooms can be stuffed ahead of time, covered and stored in.
refrigerator until time to broil.