Cook pasta according to the package directions, omitting salt and fat. Drain, reserving 1/4 cup cooking liquid.
Combine cheese, pepper, salt, egg, and egg white in a small bowl, stirring with a whisk. Gradually add the reserved 1/4 cup cooking liquid to egg mixture, stirring constantly with a whisk.
Cook pancetta in a large nonstick skillet over medium-high heat until crisp. Remove pancetta from pan, reserving drippings in pan; set pancetta aside. Add leek to drippings in pan, and sauté 4 minutes. Add garlic to pan; sauté for 1 minute. Add pasta, cheese mixture, and pancetta to pan; reduce heat, and cook 1 minute, tossing well to coat. Cook 1 minute. Sprinkle with parsley; serve immediately.