Preheat the oven to 350 and grease a 9x13 pan with butter.
Beat together butter, pumpkin, xylitol, stevia, eggs, and vanilla. In a separate bowl, mix together the remaining dry ingredients. Add the dry ingredients to the wet ingredients and mix thoroughly.
Pour batter into your greased 9x13 pan and bake for 40-50 minutes.
While cake is baking, beat together the softened cream cheese and butter. Add the vanilla, stevia, and xylitol and beat until creamy.
After the cake has cooled, frost with cream cheese frosting. If you don't devour all of it the day you make it, be sure to store in in the refrigerator.