Preheat your oven to 350 degrees
Add 2 tablespoons of olive oil, 1 chopped yellow onion and 16 ounces of ground italian sausage into a large skillet and place it over medium heat
Break up the sausage into very small pieces as it cooksÂ
Once the sausage is cooked through and the onions have softened, transfer them into a large bowl and set aside for now
Bring a large pot of water up to a rolling boil
Once the water is boiling, add a large pinch of salt and 14 ounces of jumbo shells and cook according to the instructions on the box
Drain the shells and set them aside
Add 15 ounces of whole milk ricotta, 1 large egg, 2/3 cup of finely shredded parmesan, 1/3 cup of finely chopped basil and 2 cloves of finely minced garlic to the italian sausage and onions and mix until everything is fully incorporated
Transfer the filling into a pastry bag or gallon zip lock bag (optional)
Add a layer of marinara into the base of a 9"x13" baking dish
Fill the shells about half way with the italian sausage and ricotta filling and arrange them in the baking dish in a single layer
Once the dish is filled, spoon additional marinara over the shellsÂ
Cover the entire dish with shredded mozzarella
Cover the baking dish with foil and place it in a 350 degree oven
Bake for 30 minutes covered, remove the foil and bake for an additional 15 minutes or until the cheese is melted and browned to your liking
Garnish with finely chopped parsley (optional)