In a large saucepan over medium heat, melt the butter.
Add onion, mushrooms, peppers, and garlic, cooking until vegetables are softened and golden.
Remove from heat.
Place cooked pasta in a large bowl or stock pot.
Add eggs and heavy cream, stirring until pasta is coated.
Add mozzarella, Parmesan cheese, and sausage, tossing to combine.
Stir in sauce, salt, and pepper.
Pour mixture into a greased 9-inch springform pan.
Using a spatula, press down on the pasta to ensure that the finished pie will slice neatly.
Bake at 475 degrees for 15-18 minutes, or until edges are crispy.
Cool for 15 minutes before removing sides of pan and cutting into slices.
Serve with additional pasta sauce, and a sprinkling of basil and Parmesan cheese.