Directions

1. Preheat an oven to 375 degrees F (190 degrees C).
2. Brush 30 cups in muffin pans lightly with olive oil. Brush the remaining olive oil onto the mushrooms on all sides, and place them gill-sides-up into the muffin cups.
3. Bake the mushrooms in the preheated oven until just tender, about 12 minutes. While the mushrooms are baking, beat the egg, salt, and garlic in a mixing bowl. Stir in the drained spinach, 1/4 cup Parmesan cheese, Gouda cheese, mozzarella cheese, and bread crumbs until evenly blended.
4. Remove the mushrooms from the oven, and drain off any accumulated juice. Fill the mushroom caps with the spinach mixture, and replace into the muffin pan. Sprinkle the mushrooms with the remaining 1/4 cup Parmesan cheese.
5. Return to the oven, and bake until the stuffing is hot and golden brown, about 10 minutes.