Prepare the Portabellas
1
Using a spoon, scrape out the underside (mycelium) of the portabellas. This is the filter looking part of the mushroom.
2
Arrange the portabellas in a baking casserole dish. A 9x11 baking pan works well for this.
Prepare the Sauce
1
If you have your favorite tomato sauce, please use it! I like to use a plain traditional tomato sauce and then add 1/4 teaspoon each of garlic powder, onion powder, basil, oregano, parsley, salt and pepper.
2
In a small bowl, add and mix the seasonings into the sauce.
Stuff the Portabellas
1
Preheat the oven to 350F.
2
Split your ground sausage into 4 mostly even sections. (If your portabellas are not all the same size, add or remove some sausage to even the portions.) Press 1/4 of the sausage into each portabella like a patty.
3
Add a spoonful of ricotta cheese on top of the ground sausage of each portabella.
4
Add a spoonful of sauce on top of the ricotta cheese of each portabella.
5
Add 1/4 cup of mozzarella cheese on top of each portabella. Here is what they will look like at each stage from left to right: 
6
Bake at 350F for about 35 min or until the sausage reaches an internal temperature of 160F.
7
Serve with your favorite vegetable. This pairs well with green beans!
Tips for Success
For even more flavor, use a spicy sausage!