01 -
Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper.
02 -
Brush both sides of portobello mushroom caps with olive oil and position them gill-side up on the prepared baking sheet. Bake for 10 minutes until they start to release moisture.
03 -
In a large skillet over medium heat, warm the remaining olive oil. Add minced garlic and finely chopped onion; sauté until softened, around 3 to 4 minutes.
04 -
Add the chopped spinach to the skillet and cook, stirring, until wilted, about 2 to 3 minutes. Remove the pan from heat and allow mixture to cool slightly.
05 -
In a mixing bowl, combine the cooled spinach mixture with ricotta cheese, grated Parmesan cheese, salt, black pepper, and optional nutmeg. Stir thoroughly to create a uniform filling.
06 -
Evenly spoon the spinach and cheese filling into the roasted mushroom caps. Top each cap with shredded mozzarella cheese.
07 -
Return the stuffed mushrooms to the oven and bake for 15 to 20 minutes, or until the cheeses are bubbly and golden brown.
08 -
Remove from the oven and garnish each mushroom with additional grated Parmesan cheese before serving.