In a mixing bowl start by adding the wet ingredients (oil, eggs, pumpkin and vanilla) and using an electric mixer on low beat to combine, making sure the eggs are broken up and incorporated.
Add the sugar to your wet ingredients and mix until incorporated.
In a seperate bowl combine all the dry ingredients and add them in small batches to the mixing bowl while running mixer on low. Mix until thoroughly combined for a smooth cake batter.
Spread cake batter evenly in an ungreased 12" x 17" baking sheet.
Bake in a 350° pre-heated oven for 20-30 minutes, until cake bounces back when tapped lightly and a toothpick comes out clean. Once done remove from oven and allow to cool completely.
Cream Cheese Icing
Beat together butter and cream cheese until smooth; stir in vanilla.
Add confectioners' sugar a little at a time, beating until the mixture is smooth.
Once pumpkin bar cake is completely cool frost with the cream cheese icing evenly, cut into squares to serve.