Add all the ingredients in the order listed (minus the sweet potatoes and walnuts) into the food processor or blender and blend until smooth.
Stir in sweet potatoes and walnuts. Pour batter evenly into a greased, lined or silicone 12-cup muffin pan.
Bake for 20 minutes, or until inserted toothpick comes out clean.
Cool completely (wait at least 10 minutes) before taking them out of the pan.
Once cooled, store in the refrigerator. If your cakes are on the wetter side (be sure to squeeze out as much liquid from the sweet potatoes), they will firm up a bit more in the fridge.
Notes
Dairy-free? substitute with plant-based yogurt of choice
Once cooled completely, transfer the cakes into an airtight container and store in the refrigerator for up to 4 days.