Preheat the Oven
Set your oven to 375°F (190°C). Lightly grease your 9x13-inch baking dish.
Cook the Meat Sauce
Heat olive oil in a large skillet over medium heat. Add onion and garlic; sauté until fragrant. Add ground beef and cook until browned. Stir in tomato paste, marinara, Italian seasoning, salt, and pepper. Simmer for 10 minutes.
Prepare the Ricotta Filling
In a mixing bowl, combine ricotta cheese, egg, Parmesan, and parsley. Mix until smooth and creamy.
Assemble the Lasagna
Spread ½ cup sauce on the bottom of the baking dish. Layer 3 noodles over it. Add half of the ricotta mixture, followed by a layer of sauce and mozzarella. Repeat once more, then top with remaining noodles, sauce, and mozzarella.
Bake the Lasagna
Cover with foil and bake for 25 minutes. Remove foil and bake an additional 15–20 minutes, until the top is bubbling and golden brown.
Rest Before Serving
Let the lasagna rest for at least 15 minutes before slicing. This helps it set beautifully.