Bring a large pot of water to boil and toss in the cubed sweet potato. Cook until very tender when pierced with a fork, about 10 minutes. Place in a strainer and cool.
Preheat oven to 350F and grease a large loaf pan with oil or butter.
Toss the wet ingredients - everything from the cooked sweet potato through the egg - in a blender and blend until smooth. One by one, add in the dry ingredients, blending for a few seconds each time until well incorporated. Stir in the raisins.
Pour the batter into the loaf pan and bake 40-42 minutes, or until a toothpick comes out mostly clean. Remove from oven and cool completely before slicing.
Slice and serve immediately, and store leftovers in an airtight container for up to two weeks.