PREP: Preheat the oven to 350 degrees F. Bring a large pot of water to boil. Spray a 9x13-inch ceramic or glass baking dish with nonstick spray. Spread 1 cup (245g) of the pasta sauce on the bottom of the pan and set aside.
SHELLS: Salt the water once it's boiling (I add 1 teaspoon fine sea salt to every 4 cups of water). Cook the jumbo pasta shells according to package directions for al dente, boiling for 1 minute less than the package says. I recommend boiling a few extra in case some break. Drain, rinse in cold water, and set aside.
MEATMIXTURE: Heat olive oil in a large skillet over medium-high heat. Once the oil is shimmering, add in the onion and stir for 3-5 minutes or until softened. Add in the garlic and stir for 30 seconds or until fragrant. Move veggies to the side of the pan and add in the ground beef, Italian sausage, Italian seasoning, salt and pepper to taste (I add 3/4 teaspoon salt and 1/4 teaspoon pepper). Stir and break up the meat. Cook until browned and then remove from the heat (drain any grease if needed) and set aside.
CHEESEMIXTURE: In a large bowl, mix cream cheese spread, 1 and 1/2 cups of the Italian cheese, the Parmesan and egg. Mix until combined. Add in the cooked beef/sausage mixture and stir to combine. Spoon about 2 tablespoons of the mixture into each shell. (See Note 1.)
BAKE: Place the stuffed shells on the sauce in prepared pan and then pour the remaining sauce over top, covering the shells completely. Bake for 35 minutes. Sprinkle with the remaining 1/2 cup Italian cheese and cook for 10 more minutes.
ENJOY: Remove and top with fresh parsley and basil if desired.
Note 1: To stuff the shells easily, add the cheese and sausage mixture to a gallon-sized zipper-top plastic bag. Press the cheese mixture to one side of the bag and using scissors, cut off a 1-inch opening in the corner. Squeeze the cheese mixture into each shell and gently press the mixture down to fill the shells.Makeahead: These stuffed shells with sausage can be made up to a day in advance and then baked when you're ready. If you make this recipe ahead of time, prepare them fully but do not bake them. Once ready to bake, bake for 30 minutes, covered with foil; then uncover the shells and finish baking according to the recipe directions.