Coat a 12-ounce microwave-safe coffee cup with cooking spray. Add hash browns. Microwave on high for 1 minute. In a small bowl, combine the egg, milk, sausage and cheese; pour over hash browns. Stir until blended.
Microwave on high for 30 seconds. Stir. Microwave 30 seconds longer or until eggs are set. Serve with salsa if desired.