Step 1Remove stems from mushrooms. Finely mince stems and set aside. Place mushroom caps on baking sheet. Brush caps with melted butter and season with salt and pepper. Set aside.
Step 2Cook onions and shallots in oil and any remaining butter in skillet over medium heat until tender but not browned, 3 to 4 minutes. Add minced mushroom stems to onion mixture. Raise heat to high and saute until liquid is absorbed, 4 to 5 minutes. Add Madeira and bring to boil. Boil until liquid evaporates. Cool. Add bread crumbs, Gruyere and Parmesan cheeses and parsley to mushroom mixture. Add enough cream to bind mixture. Adjust seasoning. Spoon stuffing into mushroom caps on baking sheet.
Step 3Bake at 375 degrees until hot and bubbly, 10 to 12 minutes.