Step 1: In a large skillet over medium heat, add the ground beef (or Italian sausage) and cook until browned, breaking it up with a spoon. Drain any excess fat.
Step 2: Stir in the chopped onion and minced garlic, cooking for 3-5 minutes until the onion is translucent and fragrant.
Step 3: Add the crushed tomatoes, tomato paste, dried oregano, dried basil, salt, and pepper to taste. Bring to a simmer, then reduce heat and let it gently simmer for 15-20 minutes, allowing the flavors to meld.
Step 4: While the sauce simmers, prepare the cheese mixture. In a separate large mixing bowl, combine the ricotta cheese, large egg, 1/2 cup grated Parmesan cheese, and 1 cup of the shredded mozzarella cheese. Mix until well combined. If desired, stir in the fresh parsley.
Step 5: To assemble the lasagna, spread a thin layer of the meat sauce on the bottom of a 9×13-inch baking dish.
Step 6: Place 3 lasagna noodles over the sauce. If using uncooked noodles, ensure they are slightly overlapping and fully covered by sauce in subsequent layers.
Step 7: Spread half of the ricotta cheese mixture evenly over the noodles, followed by another generous layer of meat sauce.
Step 8: Repeat the layering process: place 3 more lasagna noodles, spread the remaining half of the ricotta mixture, and then another layer of meat sauce.
Step 9: Place the final 3 lasagna noodles on top. Spread the remaining meat sauce over these noodles and sprinkle generously with the remaining 1 cup of shredded mozzarella cheese (and any additional mozzarella if desired).
Step 10: Preheat your oven to 375°F (190°C).
Step 11: Cover the baking dish tightly with aluminum foil and bake for 25 minutes.
Step 12: Remove the foil and continue to bake for an additional 15-20 minutes, or until the cheese is bubbly, golden brown, and the noodles are tender.
Step 13: Allow the lasagna to cool for about 10-15 minutes before slicing and serving. This resting period helps the layers set, making for cleaner cuts and preventing it from falling apart.
Step 14: Cut into squares and serve warm, garnished with additional fresh parsley if desired.