Cook and stir until onion begins to brown, about 5 minutes.
Add broth and apple juice. Bring to a boil, reduce heat to low; simmer 5 minutes.
Add mashed sweet potato and with an immersion blender or food processor mix ingredients until smooth.
Bring to a second boil over medium heat; whisk in yogurt. Reheat just until hot (do not boil).
Serve topped with cilantro, apple slice, pecans or chopped red pepper if desired.