Preheat oven to 400 F. degrees.
Remove the casing from the sausage and brown in a skillet. Break the sausage into crumbles as it cooks. Drain as much oil from the sausage once it is cooked through.
Place the cooked sausage in a sauce pan and add the jar of pasta sauce. Heat until simmering. Reduce heat and keep warm while preparing the rest of the ingredients.
Cook the large shells following the manufacturers directions for a baked dish. Drain the pasta and run cold water over the shells to remove some of the starch which will keep the shells from sticking together. Set aside.
Divide the mozzarella cheese in half setting one half aside for topping the stuffed shells.
In a large bowl beat the egg well.
Add half the mozzarella cheese to the bowl, and add the ricotta cheese, Parmesan cheese, parsley, salt and pepper. Mix well to combine.
Spread half of the sauce mixture into the bottom of a lasagna pan. Arrange the cooked shell pasta in a single layer in the pan.
Fill each shell with the ricotta cheese mixture.
Drizzle remaining sauce over shells and top the shells with the remaining mozzarella cheese.
Bake in a preheated oven for 20 to 30 minutes.