Bring a large stockpot of heavily salted water to a rolling boil. Add the wavy lasagna pasta sheets and cook for 8-9 minutes until slightly al dente. Drain and lay flat on parchment paper.

Heat olive oil in a skillet over medium-high heat. Add diced onion and ground beef, browning until a deep golden-brown crust forms and no pink remains.

Reduce heat, stir in garlic and tomato paste for 1 minute. Add crushed tomatoes, salt, and pepper. Simmer for 15 minutes until it becomes a thick, glossy dark red meat sauce.

In a medium bowl, combine the creamy white ricotta cheese, egg, and grated Parmesan cheese. Stir vigorously until smooth.

Preheat oven to 375°F (190°C). Spread a thin layer of sauce in a 9x13-inch baking dish. Alternate layers of 3 wavy pasta sheets, one-third ricotta mixture, meat sauce, and a sprinkle of mozzarella. Repeat twice.

Top with remaining meat sauce and generously cover with mozzarella. Cover loosely with foil and bake for 25 minutes.

Remove foil and bake an additional 15-20 minutes until the mozzarella is bubbly, melted, and slightly charred golden-brown. Rest for 15 minutes before slicing and garnishing with chopped fresh parsley.