Before starting the steps of this recipe, break the spaghetti noodles in half and follow the package instructions to boil, drain, and allow them to cool.
Preheat oven to 425 degrees F.
Spray a 9 x 13 inch baking dish with non-stick cooking spray.
In a large bowl, combine the cooled spaghetti noodles, 1/2 cup of mozzarella cheese, parmesan cheese, milk, an egg, Italian seasoning, and garlic salt.
Transfer noodle mixture to the prepared baking dish and spread it into an even layer. Place in the oven, bake uncovered for 15 minutes.
While pasta is baking, prepare the sauce. Brown Italian sausage in a large skillet over medium heat for about 8 minutes, then drain any excess grease.
Pour the marinara sauce over the cooked Italian sausage in the skillet, then mix in the Italian seasoning. Stir well to combine the sauce with the sausage.
When the oven timer for the baked pasta goes off, remove pan from the oven and lower the temperature to 350 degrees F.
Spread the meat sauce evenly over the cooked noodles in the pan, then add the remaining 2 cups of cheese on top.
Layer pepperoni slices on top of the cheese and sprinkle with a dusting of basil.
Return to the oven and bake uncovered for 25 to 30 minutes.