Prepare Sweet Potato: Preheat the oven to 350°F (175°C). Cook the sweet potato by baking, steaming, or microwaving it until tender. Mash it well and let it cool slightly.
Mix Dry Ingredients: In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
Combine Wet Ingredients: In a large bowl, whisk together the oil, granulated sugar, brown sugar, eggs, and vanilla extract until smooth. Fold in the mashed sweet potato until well combined.
Combine Mixtures: Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Do not overmix.
Pour and Bake: Pour the batter into a greased 8x4-inch loaf pan. Smooth the top, and bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean.
Cool: Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.