Step 1: In a large, oven-safe skillet (preferably cast iron), brown the ground beef and Italian sausage over medium-high heat, breaking it apart with a spoon. Drain any excess fat.
Step 2: Add the chopped onion and cook until softened, about 5 minutes. Stir in the minced garlic, Italian seasoning, salt, and pepper, and cook for another minute until fragrant.
Step 3: Pour in the marinara sauce and stir well. Bring the mixture to a gentle simmer.
Step 4: Carefully add the broken lasagna noodles to the skillet, pushing them down into the sauce to ensure they are mostly submerged. Cover the skillet and reduce heat to medium-low. Simmer for 15-20 minutes, or until noodles are tender, stirring occasionally to prevent sticking.
Step 5: While the noodles cook, prepare the cheese mixture: In a medium bowl, combine the ricotta cheese, egg, and 1/4 cup Parmesan cheese. Mix until well combined.
Step 6: Once the noodles are tender, uncover the skillet. Drop spoonfuls of the ricotta mixture over the top of the lasagna. Sprinkle evenly with the shredded mozzarella cheese.
Step 7: If your skillet is oven-safe, transfer it to a preheated oven (375°F/190°C) and bake for 10-15 minutes, or until the cheese is melted and bubbly. Alternatively, cover the skillet again and cook on the stovetop over low heat until cheese is melted.
Step 8: Remove from heat and let it rest for 5 minutes before serving. Garnish with fresh basil and extra Parmesan cheese, if desired.