Cook pasta shells in a large pot of salted boiling water according to package instructions. Drain; rinse under cold water.
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.
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.
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.
Fill the cooked, cooled pasta shells with the ricotta mixture. Arrange the shells in the baking dish.
Top the shells with the marinara sauce mixture. Sprinkle the remaining ½ cup of Italian cheese blend over top.
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!
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Notes
Boil the pasta in well-salted water. This is your only opportunity to season the pasta itself, so don't be shy with the salt!
Cook the pasta shells just until barely al dente, since they will continue to cook in the oven. You don't want to end up with overdone, mushy pasta!
Garnish the shells with fresh herbs like parsley or basil for a bright finishing touch.
This recipe yields a large batch to serve 8, so it's perfect for entertaining. If you're feeding a smaller family, you can divide the stuffed shells between two smaller 8-inch baking dishes and freeze one for later.
Use about 1 lb. of ground Italian sausage, ground turkey, or ground chicken instead of the ground beef.
To make theseamazing stuffed shells without ricotta, you can substitute with cottage cheese instead. If using cottage cheese, I recommend straining off some of the liquid first or using a whipped cottage cheese so that you don't end up with a watery filling.
Add cooked spinach to the filling. Just make sure that you squeeze the spinach very dry before stirring it into the ricotta mixture -- otherwise it will water-down the dish.