Preheat oven to 375 degrees F.
In a large bowl, cream butter and sugars together until light and fluffy.
Add eggs, one at a time, mixing after each egg.
Mix in vanilla and pumpkin.
In a separate bowl, whisk together flour, salt, baking soda, pumpkin pie spice and cinnamon.
Add wet mixture to dry ingredients and mix until combined.
Spread batter into a rimmed baking sheet (18 x 1 x 1 inch) sprayed with nonstick cooking spray.
Bake for 15-18 minutes, or until bars are light golden brown and an inserted toothpick comes out clean. Let cool.
For frosting, cream butter and cream cheese together, then add vanilla, milk and powdered sugar.
If you want the frosting to be thicker, add more powdered sugar. If you want it to be thinner, add more milk.
Spread frosting on top of cooled bars, cut into bars and serve.