Bring a pot of water to a boil. Peel and dice your sweet potato and boil until very soft. Drain.
You can run it through a food processor or blender or just mash it by hand. (Or you could just buy a can of sweet potato puree).
Preheat oven to 325 degrees. Spray your pans with baking spray.
In a stand mixer, beat the banana and sweet potato until smooth. Add the sugar, oil, and milk, mixing to combine well. Add eggs and vanilla and beat again
Dump the dry ingredients on top of the wet ingredients (with soda on top of the flour, not directly on the wet mixture). Mix until well-combined, but don't overmix.
Pour the batter into the pans about 3/4 of the way full.
Bake until a skewer comes out clean.
Let cool slightly, and then remove from pans, letting cool on a cooling rack (or eat them while they're still warm. Delicious).
Bake time for different variations: about 18 minutes for mini-muffins, 25-30 for muffins, 35-40 for mini loaves.
slightly adapted from Heather Christo Cooks