½cuppacked light brown sugarplus extra for sprinkling
1 ½cupsall-purpose flour
2teaspoonbaking powder
¼teaspoonbaking soda
1teaspoonground cinnamon
¼teaspoonground nutmeg
⅛teaspoonground clove
¼teaspoonsalt
1teaspoonpure vanilla extract
1teaspoonfreshly grated orange zest
2large egg whites
½cupmilk
⅓cupcanola or sunflower oil
½cupcoarsely chopped walnuts
Instructions
Preheat oven to 375°F and a standard 12-cup muffin pan with paper liners.
Bring a large pot of water to a boil and cook the sweet potato until very tender, about 15 minutes. Peel it and transfer to a mixing bowl. Beat with electric mixer on high speed until smooth. Beat in sugar and set aside to cool slightly.
In a medium bowl, sift together flour, baking powder, baking soda, spices and salt; set aside.
Stir vanilla extract and orange zest into sweet potato mixture. Add egg whites and beat with electric mixer on high speed until pale, thick and fluffy, about 2 minutes. Stir in milk and oil. Add dry ingredients and stir until just combined, but do not over-mix. Fold in walnuts.
Divide batter among muffin cups, filling them to the rim. Sprinkle some brown sugar on the top of each muffin. Place in the center rack of oven and bake until golden brown, about 16-17 minutes.