Step 1: Prepare the Meat Sauce : Heat olive oil in a large skillet or saucepan over medium heat. Add chopped onion and sauté until translucent, about 3–4 minutes. Add garlic and cook for 30 seconds until fragrant. Add ground beef and cook until browned, breaking it up as it cooks. Drain excess fat. Stir in crushed tomatoes, tomato sauce, tomato paste, sugar, basil, oregano, and red pepper flakes. Simmer on low heat for 20–25 minutes, stirring occasionally, until thickened. Season with salt and pepper to taste.
Step 2: Make the Ricotta Mixture : In a medium bowl, combine ricotta cheese, egg, Parmesan, parsley, salt, and pepper. Stir until smooth and well blended. Set aside.
Step 3: Cook the Lasagna Noodles : (Skip if using oven-ready noodles) Bring a large pot of salted water to a boil. Cook lasagna noodles according to package directions until al dente. Drain and lay flat on parchment paper or lightly oiled surface to prevent sticking.
Step 4: Assemble the Lasagna : Preheat oven to 375°F (190°C). Spread 1 cup of meat sauce on the bottom of a 9x13-inch (23x33 cm) baking dish. Arrange 3 lasagna noodles on top. Spread half of the ricotta mixture over noodles. Sprinkle ½ cup mozzarella. Add 1 cup of meat sauce. Repeat layers (noodles → ricotta → mozzarella → sauce). Finish with a top layer of noodles, remaining sauce, mozzarella, and Parmesan.
Step 5: Bake : Cover the dish tightly with aluminum foil (to prevent drying). Bake for 25 minutes covered. Remove foil and bake another 15–20 minutes, until cheese is melted and golden brown. Let rest for 10–15 minutes before slicing — this helps it set for perfect layers.