Preheat oven to 350 degrees and grease a 9×13 pan. In a large bowl, blend together the pumpkin, sugar, and vegetable oil. Add the eggs and blend again. In a small bowl, whisk together the flour, baking soda, pumpkin pie spice, and salt and add to the pumpkin mixture. Stir to combine and transfer to the prepared cake pan. Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean. Allow cooling completely before icing.

In the bowl of a mixer, blend together the butter and cream cheese. Add the vanilla, milk, and powdered sugar and whip until combined and fluffy. Spread in an even layer over the cake. Cut into squares and serve!