Stuffed Mushrooms

8 large fresh mushrooms 
1 tablespoon olive oil 
2 cups ricotta cheese 
3/4 cup grated Parmesan cheese 
3/4 cup shredded mozzarella cheese 
4 tablespoons pesto 

Preheat oven to 375 degrees F (190 degrees C). 
Wash mushrooms, remove stems, hollow out and brush inside and out with olive oil. 
In a medium-size mixing bowl, combine cheese and pesto, reserving 1/4 cup Parmesan cheese for later. Stuff the cheese-pesto mixture into the mushroom caps. Arrange the caps on a cookie sheet. Sprinkle the mushrooms with the reserved Parmesan cheese. 
Bake for 25 to 30 minutes, or until the cheese is bubbling and brownish.