In a large Dutch oven or heavy pot,
heat 1 tablespoon oil over medium-high.
Add onion, season with salt and
pepper, and cook until beginning to
brown around edges, about 7 minutes.
Add cumin and garlic and cook, stirring,
until fragrant, about 1 minute. Stir
in sweet potatoes, chile, and broth.
Bring to a boil; reduce to a rapid simmer,
partially cover, and cook until sweet
potatoes can be mashed easily with a
spoon, 20 to 25 minutes.
Let soup cool slightly. Working in
batches, transfer soup to a blender
and puree until smooth (use caution
when blending hot liquids). Return
pureed soup to pot over low heat and
season with salt and pepper. Top
soup with sour cream and serve with
tortilla wedges, if desired.