Step 1: Prepare the Meat Sauce
• Cook the Meat: In a large skillet over medium heat, brown the ground beef (or sausage) with the diced onion and minced garlic until the meat is cooked through. Drain any excess fat.
• Add Tomatoes: Stir in the crushed tomatoes, tomato sauce, tomato paste, oregano, basil, red pepper flakes (if using), salt, and pepper. Let the sauce simmer for about 15 minutes, stirring occasionally.

Step 2: Prepare the Cheese Mixture
• Mix Cheese Ingredients: In a bowl, combine ricotta cheese, grated Parmesan cheese, egg, parsley, salt, and pepper. Mix until well combined.

Step 3: Assemble the Lasagna
• Layer Ingredients: In a 9×13-inch baking dish, spread a thin layer of meat sauce on the bottom.
• Add Noodles: Place a layer of lasagna noodles over the sauce.
• Spread Cheese Mixture: Spread a layer of the ricotta cheese mixture over the noodles, followed by a layer of meat sauce, and then a layer of mozzarella cheese.
• Repeat Layers: Repeat the layering process (noodles, ricotta, meat sauce, mozzarella) until all ingredients are used, finishing with a layer of meat sauce topped with mozzarella and extra Parmesan cheese.

Step 4: Bake
• Cover and Bake: Cover the baking dish with aluminum foil (to prevent sticking, you can spray the foil with cooking spray) and bake in a preheated oven at 375°F (190°C) for 25 minutes.
• Uncover and Finish Baking: Remove the foil and bake for an additional 15–20 minutes, or until the cheese is bubbly and golden brown.

Step 5: Serve
• Garnish and Enjoy: Let the lasagna cool for about 10 minutes before slicing. Garnish with fresh basil if desired. Serve hot.