Preheat oven to 350 degrees. Prepare muffin tins by spraying with non-stick cooking spray. (recipe makes about 3 dozen muffins). Combine dry ingredients (first six ingredients) in a large bowl and whisk until blended. In a separate bowl, combine next 5 ingredients (milk through butter) and whisk until well blended. Pour wet ingredients into dry ingredients and stir with a spoon just until blended. Stir in sweet potato and allspice until well blended. Fill prepared muffin tin cups about 2/3 full. Bake in preheated oven at 350 degrees for approximately 15 minutes, just until edges are lightly browned and toothpick comes out clean.