Preheat the oven to 375°F (190°C). Grease a 9x13-inch baking dish.
Cook the ziti pasta according to package instructions until al dente. Drain and set aside.
In a large skillet over medium heat, cook the ground beef until browned. Drain excess fat.
Add the marinara sauce to the beef and simmer for 5 minutes.
In a large bowl, combine ricotta cheese, sour cream, egg, Parmesan cheese, salt, and pepper.
Spread half of the cooked ziti in the prepared dish.
Top with the ricotta mixture, then half of the meat sauce, and sprinkle 1 cup of mozzarella.
Repeat the layers with remaining ziti, meat sauce, and mozzarella.
Cover with foil and bake for 30 minutes. Remove foil and bake an additional 10-15 minutes until bubbly.
Garnish with chopped parsley if desired before serving.