A small amount of the pasta's cooking liquid is whisked into the egg mixture to prevent the eggs from overcooking when added to the hot pasta. This procedure, called tempering, results in a rich, creamy sauce that easily coats the noodles.
4 servings (serving size: 1 1/4 cups)
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.