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.
To prepare crepes, place egg, egg whites, and milk in a blender; process 15 seconds.
Let stand 8 minutes.
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.
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.