I found this in More Muffins by Barbara Albright & Leslie Weiner. I tried it this afternoon...yummy!
1 3/4 cups all-purpose flour 3/4 cup firmly packed light brown sugar 2 tsp baking powder 1/4 tsp baking soda 1/4 tsp salt 1/2 tsp ground cinnamon 1/4 tsp ground ginger 3/4 cup mashed baked sweet potato, cooled 1/2 c FF milk, at room temperature (I used soy) 2 large eggs (at room temperature), lightly beaten (I used 1/3 c All Whites, or 4 egg whites) 3 T canola oil 1 1/2 tsp vanilla 1/4 to 1/3 c. finely chopped crystallized ginger
1. Preheat oven 375 F. Lightly coat twelve 2 5/8" x 1 1/8" (about 3 oz.) muffin cups with nonstick cooking spray.
2. In a large bowl, stir together flour, sugar, baking powder, baking soda, salt, cinnamon, and ground ginger. In another bowl, stir together sweet potato, milk, eggs, oil, & vanilla until blended. Make a well in center of dry ingredients; add milk mixture & stir just to combine. Stir in crystallized ginger.
3. Spoon batter into prepared muffin cups. Bake for 15-20 min., or until a toothpick inserted in center of one muffin comes out clean.
4. Remove muffin pan to wire rack. Cool for 5 min before removing muffins from cups; finish cooling on rack. Serve warm or cool completely and store in an airtight container at room temperature.