Preheat oven to 325°F

Combine spinach, salt & pepper, and cheeses (while saving 1 tablespoon of parmesan) into a small mixing bowl

clean gills out of mushroom cap, rinse and bake for 10 minutes

drain liquid out of mushroom when done baking

Spread cheese and spinach mixture in mushroom cap, filling the whole mushroom, spinkle with remaining parmesan cheese

Bake for 15 minutes or until golden on top