They may be small, but these mushroom bites are loaded with huge flavor!
Preheat oven to 425° F.
Remove stems from cremini mushrooms and finely chop. Reserve caps.
In a sauté pan, cook pancetta until golden brown and crispy. Pour off excess fat.
Add mushroom stems, onions, garlic and rosemary and sauté until mushrooms are soft. Remove from heat and let cool to room temperature.
Add egg, breadcrumbs and shredded Gouda, grated Parmesan, shredded Cheddar, shredded Provolone and cream cheese and mix well.
Fill each mushroom cap generously with the filling mixture. Place on sheet tray and bake until filling is cooked through and golden brown on top, about 8-10 minutes.