Ricotta Mixture: In a medium bowl, add 15 ounces whole milk ricotta cheese, ¼ cup spinach leaves, ¼ cup parmesan cheese, ¼ cup mozzarella cheese, 1 egg, 2 tablespoons fresh basil, 2 tablespoons pesto, 1 tablespoon Italian seasoning, 1 teaspoon lemon juice, 1 teaspoon kosher salt, and ⅛ teaspoon ground black pepper; stir to combine and set aside.
Pasta: Cook 12 ounces jumbo pasta shells al dente according to package instructions. Drain and toss with a little olive oil if they might sit out for a bit while you prepare the sauce - this will help prevent them from sticking and drying out.
Make Meat Sauce: Meanwhile, bring a large cast iron skillet to medium-high heat. Add 1 tablespoon olive oil and swirl to coat the pan. Add 2 teaspoons garlic and move around pan until it becomes fragrant, approx. 30 seconds. Add 1 pound ground beef and move around pan until it is fully cooked; drain excess grease. Add 24 ounces marinara sauce, onion, 2 tablespoons fresh basil, ½ teaspoon kosher salt, ⅛ teaspoon ground black pepper. Stir to combine. Taste and add any additional salt, as desired.
Fill Shells: Add approx. 1/2 the meat sauce to the bottom of a 9x13 baking dish. One by one, take a shell and fill it with the ricotta mixture. Place in the pan and repeat until the ricotta mixture is all used up.
Bake: Cover the shells with the remaining meat sauce and then top with 2-3 cups mozzarella cheese. Cover pan with foil and place in the oven, middle rack, for 30 minutes. Remove foil and return to oven for 5-10 minutes or until cheese is melted.
Serve: Let cool slightly and then serve. Feel free to top with additional fresh basil and parmesan cheese.
Notes
Dairy-Free: To make this dish dairy-free, use dairy-free cheese options throughout.
Gluten-Free: To make this dish gluten-free, use gluten-free pasta shells.
Storage: Once cooled completely, store in an air-tight container in the fridge for 3-5 days.
Spice it up: For those with a brave palette, feel free to throw in some red pepper flakes over the top or sprinkle in some cayenne pepper to the marinara sauce.