Preheat oven to 350F and grease a 10x15x1 inch jelly roll pan or line it with parchment paper.
Combine the flour, salt, baking soda, baking powder, and spices in a large bowl then whisk together and set aside.
In a separate bowl combine the eggs, oil, white and brown sugar, vanilla, milk, and pumpkin puree then whisk together until smooth.
Pour the wet mixture into the dry and mix until just combined then transfer the batter to your prepared pan and spread out into an even layer using an offset spatula. Bake at 350F for about 25 minutes or until the center springs back when pressed lightly.
Make the frosting by beating room temperature cream cheese and butte together until combined then add the powdered sugar and vanilla. Beat on low then switch to high for about three minutes or until light and creamy. scrape the bowl down and mix once more.
Once the base is cool cover with the cream cheese frosting, cut and serve. I like to garnish with a sprinkle of cinnamon but sprinkles
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Notes
Measure your flour correctly! Adding too much flour to the recipe is the most common mistake. The best, and easiest way to measure flour is by using a scale. If you don't have one then fluff your flour with a spoon, sprinkle it into your measuring cup, and use a knife to level it off.
Do not over-mix the batter as it will give you a denser and more tough pumpkin bar.
You can add chopped nuts, chocolate chips, sprinkles, or candy pumpkins as decoration on top of the bars.
These bars are delicious without frosting too, you can dust with powdered sugar or drizzle with caramel or icing.
You can definitely use different sized pans to make these! A 9x13 inch pan will give you a slightly thicker bar while a larger sheet pan should probably be sectioned off with foil to make a smaller area for the batter.