Preheat the oven to 350°F and grease a 10x15-inch jelly roll pan and line it with parchment paper.
In a large bowl, whisk to combine the flour, salt, baking soda, baking powder, and spices.
In a separate bowl combine the eggs, oil, white and brown sugars, 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 for 20 to 25 minutes or until the center springs back when pressed lightly.
In the bowl of a stand mixer with the paddle attachment, beat the butter on medium speed until creamy, about 30 seconds. Add the cream cheese and beat until creamy and combined, about 1 minute. Add the powdered sugar and vanilla. Beat on low until combined, then beat on high for about 3 minutes until light and creamy. Scrape the bowl down and mix once more.
Once the bars are cool, cover with the cream cheese frosting, cut and serve. I like to garnish with a sprinkle of cinnamon or festive sprinkles.
