1. To prepare filling, cook sausage and onion in a large nonstick skillet over medium-high heat 9 minutes or until browned, stirring to crumble. Add cream cheese to sausage mixture, stirring until melted. Stir in sour cream. Remove pan from heat; cover and keep warm.
2. To prepare crepes, place egg, egg whites, and milk in a blender; process 15 seconds. Let stand 8 minutes.
3. Heat an 8-inch crepe pan or nonstick skillet over medium heat. Coat pan with cooking spray. Pour about 2 tablespoons egg mixture into center of pan; quickly tilt pan in all directions so batter covers pan with a thin film. Cook about 1 minute or until edges are dry, batter is almost set, and bottom is brown. Carefully lift edge of crepe with a spatula to test for doneness. Turn crepe over, and cook an additional 20 seconds. Remove to a plate. Repeat procedure 7 times with remaining batter.
4. Spoon about 1/4 cup filling into center of the less-browned side of each crepe. Fold sides over filling; roll up. Place 2 filled crepes, seam sides up, on each of 4 serving plates. Garnish with chopped fresh parsley, if desired. Serve immediately.
The amount of batter needed is a little less than 2 tablespoons per crepe, so use shallow scoops of batter to ensure you get 8 crepes.