Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan.
In a large mixing bowl, combine the mashed sweet potatoes, granulated sugar, brown sugar, vegetable oil, eggs, and vanilla extract. Mix until well combined.
In a separate bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt.
Gradually add the dry ingredients to the sweet potato mixture, stirring until just combined. Be careful not to overmix.
If using, fold in the chopped nuts and raisins or dried cranberries.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean. If the top starts to brown too quickly, cover it loosely with aluminum foil.
Allow the bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.