Pre-heat oven to 350.
Wash all mushrooms thoroughly and remove stems so centers are hollow(great for stuffing!)
Keep the stems and finely chop them up.
Place sausage patties in a skillet and brown on both sides (about 7 minutes a side until thourougly cooked.
Finely chop sausage patties.
Line cookie sheet with aluminum foil and place mushrooms next to each other until pan is full.
Add chopped sausage and chopped mushroom stems into each individual hollowed out mushroom.
Sprinkle each mushroom with mozzarella cheese.
Bake in the oven for about 30 minutes.
The sausage has already been cooked so at this point you are just cooking until the mushrooms are soft.
Add more mozzarella once they are done and set on top of the oven, letting the cheese melt. Serve hot!