Pierce the yam with a fork and cook in the microwave until it is very soft. If you don't have/use a microwave, place the pierced yam on a foil-lined sheet pan and cook in a 400-degree oven for 45 -60 minutes until very soft. Cool.
Scoop the yam flesh into the bowl of a food processor and add 1 cup stock. Puree.
In a large soup pot, combine the pumpkin puree, yam puree, the garam masala, and the stock. Stir to combine.
Bring to a boil over medium-high heat. Reduce heat to a simmer and simmer for 10 minutes.
Add the peanut butter. Stir until well combined
Taste and season with salt and white pepper.
Ladle into bowls and garnish with a dollop of Greek yogurt and chopped peanuts if desired.
Although I don't normally specify brands, I have tried this soup with other canned pumpkin purees and it was not as good - Libby's still has the best flavor. However, if you have homemade puree or another brand that you love, absolutely use it!
I have also called for garam masala, an indian spice blend. If you don't have it, substitute pumpkin pie spice.
The addition of maple syrup is completely optional. If the yam is very sweet, you probably won't need to add it. I generally taste the soup before adding it.
For a smoother soup, you can puree the soup again after adding the peanut butter - either with an immersion blender or a regular blender. If using a regular blender, let the soup cool a bit before blending. I've made this soup without pureeing the yam and you can do that, but you will end up with a chunkier soup.
If the soup is thicker than you like, you can add a bit more stock. Start with ½ cup additions until you reach the desired consistency.
This peanut soup recipe can be made 3 days ahead of time. Cool, cover and refrigerate.
To re heat, transfer the soup into a saucepan and re heat over medium heat, stirring occasionally until hot.