01 - Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper or lightly grease it.
02 - Place the mushroom caps, cavity side up, onto the prepared baking sheet.
03 - Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the minced garlic and sauté until fragrant, approximately 30 seconds. Introduce the chopped spinach and cook, stirring, until it wilts, about 1 to 2 minutes. Remove the skillet from the heat.
04 - In a mixing bowl, combine the cooked spinach and artichoke hearts with softened cream cheese, 1/3 cup grated Parmesan cheese, shredded mozzarella cheese, sour cream, salt, black pepper, and optional red pepper flakes. Mix thoroughly until a smooth, well-combined filling is achieved.
05 - Generously spoon the prepared filling into each mushroom cap, creating a slightly mounded top.
06 - Sprinkle the tops of the stuffed mushrooms with the additional 2 tablespoons of grated Parmesan cheese.
07 - Bake for 20 to 25 minutes, or until the mushrooms are tender and the filling is golden brown.
08 - Remove the stuffed mushrooms from the oven and allow them to cool slightly. If desired, sprinkle with fresh parsley. Serve warm.