1
preheat oven to 400F. With a damp paper towel, wipe mushroom caps clean.
2
With a pastry brush, brush sides of each mushroom with olive oil; sprinkle with thyme and salt.
3
Bake mushrooms until completely softened, about 25 minutes.
4
Meanwhile, in a medium skillet, cook sausage over medium heat, breaking up with a spoon, until no longer pink, about 5 minutes; drain off excess oil.
5
Increase oven to broil. With a metal spatula, turn mushrooms over so they are stem-side up.
6
Sprinkle equal amounts of sausage, stems ,mozzarella and Parmesan onto each mushroom; broil mushroom pizzas until cheese is browned and bubbly, about 3 minutes. Sprinkle pizzas with parsley, if desired; serve immediately.