Preheat the oven to 350 degrees Fahrenheit. Spray a 13 x 9-inch baking dish with nonstick cooking spray and set aside.
Bring a large pot of salted water to a boil and cook 10 manicotti 1-2 minutes less than the package directions specify. Drain and rinse under cold water.
Heat 1 tablespoon olive oil in a large pan over medium heat. Add 1 pound Italian sausage, cook and crumble until no longer pink. Add ½ small diced onion and cook for 2-3 minutes, or until the onion begins to soften. Add 3 teaspoons minced garlic and cook for 30 seconds longer. Remove from the heat and set aside.
To a large bowl, add 15 ounces ricotta cheese, 1 large egg, 1.5 cups mozzarella cheese, ½ cup parmesan cheese, ¼ cup chopped basil, 2 teaspoons Italian seasoning, and salt and pepper to taste. Add the sausage mixture and stir to combine.
Stuff the manicotti with the cheese mixture using a spoon or piping bag.
Spread about 1 cup of the 1 (24-ounce) jar marinara sauce on the bottom of the baking dish. Line the manicotti into an even layer. Cover with remaining sauce and remaining 1.5 cups mozzarella cheese. Bake for 25-30 minutes until the cheese is melted and bubbly.
Notes
Storage, Reheating, & Make Ahead Instructions
Fridge: Store leftovers in an airtight container in the fridge for up to 5 days.
Reheat: Heat in the microwave in 30-second increments until heated through.
Freezer: This is a great recipe to freeze. Wrap the dish tightly and store it in the freezer for up to 3 months. You can bake the manicotti from frozen, just add about 20 minutes to the cook time.
Make Ahead: This can be made up to 24 hours in advance and stored in the fridge until ready to bake.