Pizza casserole deluxe

Casseroles Italian cuisine

1 (1-lb.) package ground mild Italian sausage 2 garlic cloves, minced 1 tablespoon olive oil 1 (26-oz.) jar marinara sauce 1 teaspoon kosher salt, divided ½ medium-size red onion, chopped ½ medium-size red bell pepper, chopped ½ medium-size green bell pepper, chopped ½ (8-oz.) package sliced baby portobello mushrooms 1 cup sliced black olives ½ cup pepperoni slices, chopped 1 (16-oz.) package rigatoni pasta 3 tablespoons butter 3 tablespoons all-purpose flour 3 cups half-and-half 8 ounces fresh mozzarella, shredded (2 cups) ½ cup grated Parmesan cheese ½ teaspoon freshly ground black pepper 1 (8-oz.) package shredded mozzarella cheese 8 to 10 pepperoni slices