Bake sweet potato until tender (about an hour) and allow to cool, or use leftovers if you have them on hand.
Place 3/4 cup mashed sweet potato along with all the remaining ingredients (except the baking powder) in a blender. (Make sure you measure the sweet potato as the texture will change if you add a different amount.) Blend on high until smooth.
Add the baking powder and blend on low until just combined.
Pour the batter into the muffin tin, filling each cup 3/4 of the way full.
Bake in preheated oven for 18-20 minutes until a toothpick inserted in the center of a muffin comes out clean.