Preheat the oven to 350°F and line a rimmed baking sheet with parchment paper.
Using a damp paper towel, gently clean the outside of each mushroom cap, then remove the stems. Arrange the caps upside down on the baking sheet and set aside. Add the stems and the garlic cloves to the bowl of a food processor fitted with the metal blade, and process until finely minced. (Alternatively, you can just chop the mushroom stems and garlic finely.)
24 whole fresh button mushrooms, 3 cloves garlic
Warm the oil in a skillet over medium heat. Add the chopped mushroom stems and garlic and cook for 5-7 minutes, until all moisture has evaporated, then reduce heat to medium-low. Stir in the cream cheese, Parmesan, onion powder, cayenne, and black pepper. Once the mixture is smooth, remove from the heat.
2 teaspoons olive or vegetable oil, 8 ounces cream cheese, 1/2 cup grated Parmesan cheese, 1/4 teaspoon each onion powder, cayenne pepper, and black pepper
Use a small spoon to stuff each mushroom cap with a generous amount of filling. (If preparing in advance, mushrooms can be refrigerated at this point for up to 24 hours.)
Sprinkle bread crumbs on top, if you like, then bake mushrooms for 15-20 minutes, until they are piping hot and you begin to notice liquid under the caps. Serve immediately.
bread crumbs for garnish