Preheat your oven to 375F. Boil water in a large pot and add in your shells and salt. Cook a few minutes short of al dente, according to instructions on the package. Once done, strain them and cover with cold water and set aside.
Cheese Filling
In a large bowl, combine your ricotta, 2 cups of mozzarella, ½ cup of parmesan, asiago cheese, ½ cup chopped parsley, salt, pepper, garlic powder and your Italian seasoning and combine.
Italian Sausage
Add a teaspoon of olive oil to your pan on medium high heat. Let heat for 3 minutes and add in your Italian sausage. If using a different meat, see note below.
Put the heat down to medium and spread the sausage and leave it untouched for 4 minutes so it browns on one side.
Once the 4 minutes has passed you can mix and break up the sausage. Once all the pink is gone and the sausage is browned, set it aside and let it cool for 10-15 minutes.
Stuff Shells
Place half your marinara sauce on the bottom of your casserole dish.
I like to use a large soup spoon to stuff my shells.
Stuff your shells and place them in a single layer.
Top with the rest of your marinara, mozarella cheese, and parmesan cheese.
Cover with foil and bake for 40 minutes. Remove the foil and then broil for two minutes. Top with parsley and enjoy!
Italian Sausage Sub: If you are using ground beef, chicken, turkey or a plant-based ground meat, sauté one garlic clove on medium for 30 seconds and then add in your meat, 1 teaspoon of Italian seasoning, ½ teaspoon onion powder and ½ teaspoon of ground fennel (optional but adds great taste). Cook on medium until browned.