Prepare meat sauce: In 4-quart saucepan, cook sausage, ground beef, and onion over high heat, breaking up sausage and meat with side of spoon, until meat is well browned. Discard fat. Add tomatoes with their juice, tomato paste, and 1 teaspoon salt. Heat to boiling, breaking up tomatoes with side of spoon. Reduce heat; cover and simmer, stirring occasionally, 30 minutes.
Meanwhile, in large saucepot, cook lasagna noodles as label directs but do not add salt to water. Drain and rinse with cold running water. Return to saucepot with enough cold water to cover.
Preheat oven to 375°F. In medium bowl, stir ricotta, egg, parsley, remaining 1⁄4 teaspoon salt, and pepper until well combined.
Drain noodles on clean kitchen towels. In 13" by 9" baking dish, arrange 6 lasagna noodles, overlapping to fit. Spread with all of ricotta mixture and sprinkle with half of mozzarella; top with half of meat sauce. Cover with remaining 6 noodles and spread with remaining meat sauce. Sprinkle with remaining mozzarella.
Cover lasagna with foil and bake 30 minutes. Remove foil and bake until sauce is bubbling and top has lightly browned, about 15 minutes longer. Let stand 15 minutes for easier serving.