How to Make It
Cook pasta according to the package directions, omitting salt and fat. Drain pasta in a colander over a bowl, reserving 1/4 cup cooking liquid.
Combine milk and next 4 ingredients (through pepper) in a small bowl; set milk mixture aside.
Heat a medium nonstick skillet over medium-high heat. Coat pan with cooking spray. Add pancetta to pan; sauté 3 minutes or until lightly browned. Add onion and garlic to pan; sauté 3 minutes or until onion is lightly browned. Reduce heat to medium-low. Add milk mixture and pasta to pan; toss gently to coat.
Place egg in a small bowl; stir with a whisk. Gradually add 1/4 cup reserved hot cooking liquid, stirring constantly with a whisk. Gradually add egg mixture to pan, stirring constantly; cook 4 minutes or until sauce is thick and creamy.