This is my Mom's recipe, and we love love love these. This makes plenty of stuffing, so you really have to cram it in the mushroom caps. Tonight I used fresh cilantro instead of parsley because that is what I had on hand.
1 stick butter
1/2 c bread crumbs
1 T parsley
1 T onion, chopped
1/2 tsp salt
1/2 tsp pepper
1 egg, lightly beaten
1) Preheat oven to 375 degrees.
2) Remove mushroom stems and finely chop.
3) Melt butter in skillet and saute mushroom stems, bread crumbs, parsley and onion.
4) Add salt and pepper.
5) Remove skillet from heat; mix in egg.
6) Place mushroom caps in lightly greased pan; stuff with filling.
7) Sprinkle with parmesan cheese.
8) Bake for 15 mins.