In a large stock pot, heat oil over medium heat, then add the chopped onion and grated ginger. Cook until the onion is translucent, stirring frequently (approximately 3 minutes).
Add the apples and celery, stirring to coat with remaining oil. Cook for 5-7 minutes while preparing the sweet potatoes.
Add the sweet potatoes and vegetable broth, then bring to a boil. Reduce heat once boiling, and partially cover with a lid. Simmer until the sweet potatoes are fork tender, 30-45 minutes, depending on the size of the sweet potato pieces. Add the chipotle pepper.
If using a pressure cooker or instapot instead, add all prepared ingredients to the pot and set to cook on high pressure for 6 minutes (or follow directions in your instapot recipe book). Once the pressure valve releases, the soup is done.
Use an inversion blender to purée until smooth, or alternatively purée in a blender or food processor in batches. Season with salt and pepper, according to taste.
Serve warm, garnished with grated fresh ginger and a swirl of sour cream, if desired.