Directions
Preheat your oven to 400°F / 200°C.
Line a large baking sheet with aluminum foil or parchment paper.
Gently wipe the mushrooms clean with a damp paper towel and carefully remove the stems.
In a medium bowl, beat the softened cream cheese, mayonnaise, sour cream, and garlic salt until smooth and well combined.
Fold in the chopped artichoke hearts, dry spinach, mozzarella cheese, and the 3 tablespoons (45 ml / 1.5 fl oz) of Parmesan cheese.
Mix until everything is evenly distributed.
Arrange the mushroom caps hollow-side-up on the prepared baking sheet. Spoon about 1 tablespoon (15 ml / 0.5 fl oz) of the spinach-artichoke mixture into each mushroom cap, mounding it slightly.
Sprinkle the tops with a little extra shredded Parmesan cheese.
Bake for 20 minutes, or until the filling is hot, bubbly, and lightly golden on top.
Serve warm.
Squeeze as much liquid as possible from the thawed spinach using your hands or a cheesecloth. This is the key to preventing a watery filling.