01 - Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
02 - Clean mushrooms, remove the stems, and finely chop the stems for the filling.
03 - Toss mushroom caps with olive oil, a pinch of salt, and black pepper. Arrange cavity-side up on the prepared baking sheet.
04 - Melt butter in a skillet over medium heat. Sauté minced garlic, diced shallot (if using), and chopped mushroom stems for 2–3 minutes until softened.
05 - Add shrimp to skillet and cook for 2–3 minutes until pink and opaque. Remove from heat and chop shrimp into small pieces.
06 - In a mixing bowl, combine the shrimp mixture with heavy cream, grated Parmesan, cream cheese, parsley, black pepper, and nutmeg (if using) until creamy.
07 - Spoon the shrimp Alfredo filling evenly into each mushroom cap.
08 - Top each mushroom with grated mozzarella and sprinkle with breadcrumbs, if using.
09 - Bake for 15–18 minutes, until mushrooms are tender and topping is golden brown.
10 - Garnish mushrooms with extra parsley and serve warm.