Spiced Sweet Potato Muffins

Ingredients

• 1 1/2 cup all-purpose flour
• 1 cup cold mashed sweet potatoes (prepared without milk and butter)
• 3 teaspoons grated orange peel
• 2 eggs, lightly beaten
• 1 1/2 teaspoon baking powder
• 1 teaspoon ground ginger
• 1/4 teaspoon baking soda
• 1/4 teaspoon ground cinnamon
• 1/4 teaspoon salt
• 1 cup plus 1 tablespoon sugar, divided
• 1/2 cup butter, softened
• 2 tablespoons finely chopped crystallized ginger