Step 1

Preheat oven to 350°F.

Step 2

Cook pasta shells in a large pot of salted boiling water according to package instructions. Drain; rinse under cold water.

Step 3

Meanwhile, brown ground beef and onion in a large skillet over medium-high heat. Drain off fat; let cool slightly before adding to the filling.

Step 4

Combine 1 ½ cups of the shredded Italian blend cheese, all of the ricotta cheese, all of the Parmesan cheese, the egg, the pesto, and half of the beef and onion mixture in a large bowl. Set aside.

Step 5

Spread ¾ cup of the marinara sauce in the bottom of a 13 x 9-inch baking dish. In a bowl, stir together the remaining marinara sauce and the remaining half of the beef and onion mixture. Set aside.

Step 6

Fill the cooked, cooled pasta shells with the ricotta mixture. Arrange the shells in the baking dish.

Step 7

Top the shells with the marinara sauce mixture. Sprinkle the remaining ½ cup of Italian cheese blend over top.

Step 8

Cover the dish with foil. Bake for 30 minutes. Remove the cover and bake for 10 more minutes. Garnish with fresh parsley or basil, if desired. Serve!