Cook broccoli in chicken broth in 2-quart saucepan with onion, margarine, salt and nutmeg according to package directions.
Combine milk and corn starch in blender container. Add broccoli mixture. Cover and blend at low speed until smooth. Return to saucepan.
Bring to boil over medium heat, stirring constantly; boil 1 minute. Remove from heat. For richer flavor stir in cheese until melted. Garnish with sour cream if desired.