Preheat oven to 425°F. Spray a muffin tin with vegetable cooking spray, or use liners.
In a large bowl, combine the first six ingredients, stirring well.
In a second bowl, combine the next four ingredients, stirring well.
Make a well in center of the dry ingredients. Add the sweet potato mixture and stir just until mixture is combined and dry ingredients are incorporated.
Fill muffin cups two-thirds full. Combine remaining 1/4 cup sugar and cinnamon. Sprinkle over each muffin. Bake for 20 to 25 minutes, or until a toothpick inserted in muffin center comes out clean. Cool in tins for 5 minutes; then turn out muffins on wire racks. Makes about 16 muffins.
Note: Lightly toasting the pecans will make a big flavor difference. To toast whole pecans, spread them out on a baking sheet and toast at 350°F for 4 or 5 minutes, or until you begin to smell them. Pecan pieces or chopped pecans will take less time to toast.