In a large mixing bowl, combine the sugar, oil, pumpkin and eggs. In another bowl, whisk the flour, baking soda, salt, baking powder and cinnamon together; add to pumpkin mixture and beat until well mixed.

Fill paper-lined muffin cups two-thirds full. Bake at 350 degrees for 18-22 minutes or until a toothpick comes out clean. Cool for 10 minutes before removing from pans to wire racks to cool completely.

For frosting, place ingredients in a bowl and blend until smooth and well combined. Use to frost on top of the cooled cupcakes. Makes 24 cupcakes.