- Cook sweet potatoes until very soft. (See How to cook Sweet potato in the microwave.) 
- Scoop out the flesh to fill 2 cups and mash with a fork or potato masher. Set aside. 
- Coarsely chop pecans. 
- Preheat oven to 180°C, brush 20 to 24 muffin cups with butter or oil, or line with paper liners. 
- Sift and mix together, flour, salt, baking powder, baking soda, cinnamon, ginger and nutmeg, in a bowl. 
- In another bowl, mix together eggs, vegetable oil, butter. 
- Add sugar, brown sugar, chopped pecan or cashew nuts (leave some for decoration) and sweet potato. 
- Add the flour mixture to the sweet potato mixture and stir to just combine. 
- Fill muffin cups up to three-quarter full. 
- Sprinkle reserved nuts on top of muffins. 
- Bake for 25 minutes, until a skewer inserted into the middle, comes out clean. 
- Cool in cups for 5 minutes then remove and cool completely on a wire rack. 
- Baking Sweet potato muffins mix in a Loaf pan: