Preheat a 4-quart soup pot over medium heat. Saute the onions in oil with a pinch of salt for about 3 minutes, until translucent. Add ginger and red pepper flakes, and saute another minute or so.Add yams, veggie broth and salt. Cover and bring to a boil. Once boiling, lower heat a bit to a slow simmer and cook until potatoes are tender – usually 5 more minutes or so.
Once tender, add the vanilla beans. Use an immersion blender to puree the soup until smooth. Or transfer the soup in batches to a blender or food processor to puree. Be sure to let the steam escape in between pulses so that the steam doesn’t build up and explode all over you. Then transfer the soup back to the pot.
Add maple syrup and lime and taste for salt. Thin with a little water, if necessary. You can eat immediately, but the flavor develops a lot as it sits. The lime mellows out and the vanilla becomes more pronounced, especially the next day. Serve garnished with lime, if you like. You may also want to do a coconut swirl, or something like that, if you’re feeling fancy.