Preheat the oven to 350 degrees.
In a mixing bowl, combine the brown sugar, pumpkin puree and eggs, stirring well.
In another bowl, combine the flour, baking soda, baking powder, and spices, stirring to combine.
Add the dry ingredients to the pumpkin/egg mixture. Whisk together.
Stir in the melted butter.
Pour into a 10-1/2 x 16 inch jellyroll pan.
Bake until the cake springs back when lightly touched - about 40 minutes
Cool completely before frosting.