Step 1: Cook the Pasta Shells : Bring a large pot of salted water to a boil. Add jumbo shells and cook until just al dente (about 8–9 minutes). Drain and rinse under cold water to stop cooking. Set aside on a parchment-lined tray so they don’t stick together.

Step 2: Prepare the Filling : In a large skillet, cook ground beef over medium heat until browned. Add minced garlic and sauté for 1 minute. Stir in chopped spinach and cook until wilted (or warmed through if using frozen spinach). Remove from heat and let it cool slightly. In a large mixing bowl, combine ricotta, mozzarella, Parmesan, egg, onion powder, Italian seasoning, salt, and pepper. Add the cooked beef and spinach mixture to the bowl and stir until well combined.

Step 3: Stuff the Shells : Spread 1 cup of marinara sauce on the bottom of a 9x13-inch baking dish. Using a spoon, fill each shell with about 2 tablespoons of the filling mixture. Arrange stuffed shells in a single layer in the dish.

Step 4: Assemble and Bake : Pour the remaining marinara sauce evenly over the shells. Sprinkle the top with mozzarella and Parmesan cheese. Cover the dish with foil and bake at 375°F (190°C) for 25 minutes. Remove foil and bake uncovered for an additional 10 minutes, until cheese is golden and bubbly.

Step 5: Rest and Serve : Let the stuffed shells rest for 5 minutes before serving. Garnish with fresh parsley or basil, and enjoy warm!