Bring a large pot of water to boil. Add your shells and cook them according to the package directions. Drain, rinse off and set aside.

Cook your ground beef in a large skillet over medium high heat until cooked completely. Stir in 1 cup of your marinara sauce. Set aside.

Preheat your oven to 350 degrees.

In a medium sized bowl, combine your ricotta, Parmesan, egg and 1 cup of your mozzarella cheese.

Mix your ground beef into the cheese mixture.

Pour 1/2 cup of your marinara sauce into the bottom of a 9x13 baking pan (mine actually filled a 9x13 and a 8x8)

Spoon about 2 tablespoons of the mixture into each shell to fill them.

Place each shell into your baking pan and repeat until shells are filled with all of the mixture.

Pour remaining 1 1/2 cups of your marinara sauce over your shells.

Sprinkle tops generously with remaining mozzarella.

Cover with foil and bake for 20 minutes.

Uncover and bake for an additional 5 minutes until the cheese is fully melted.