Boil a large pot of water and add your pasta. Cook according to the package directions. Drain the noodles and set aside.
Preheat your oven to 350 degrees. Spread 1/2 cup of your tomato sauce in the bottom of a 9x13 dish.
Heat a large skillet over medium heat. Add the sausage and cook until browned. Stir in 1 cup of your tomato sauce and set aside.
In a small bowl stir together the ricotta, 1/2 a cup of mozzarella, Parmesan, egg, and spinach until fully combined. Mix the cheese directly in with your sausage.
Spoon a hearty amount of the filling into each shell. Place into your prepared baking dish and continue until all are filled. Smoother with the remaining 1/2 cup of sauce and generously sprinkle with mozzarella.
Cover with foil and bake for 20 minutes. Uncover and continue to bake for an additional ten minutes or until the cheese is melted and bubbly.