Preheat oven to 350 F. In a large mixing bowl, mix together mashed sweet potato, brown sugar, eggs, orange juice, and orange zest.

Sift together the flour, baking powder, baking soda, salt, cinnamon, and mace, and stir into the sweet potato mixture. Add in cranberries and nuts.

Spray a standard muffin tin with cooking spray and spoon the batter into the cups. Bake for 20 to 22 minutes, or until toothpick inserted comes out clean. Let cool on a rack and serve.