Preheat the oven to 350 F (177 C). Lightly grease a 15 x 10 pan jelly roll pan.
In a mixing bowl, whisk the flour, baking soda, baking powder, ground cinnamon, pumpkin spice and salt together until well combined.
2 cups (240 g) all purpose flour, 1½ teaspoons baking powder, 1 teaspoon baking soda, 2 teaspoons ground cinnamon , 1 teaspoon pumpkin spice
In another bowl whisk the oil, light brown sugar, sugar, maple syrup, canned pumpkin eggs, and vanilla extract together until smooth and well combined. Whisk the dry ingredients into the wet well combined with no visible pieces of flour. Pour the pumpkin bar batter into the prepared pan. Use a flexible spatula to smooth the batter evenly across the pan. 1 cup (240 ml) neutral baking oil , 3 large eggs, room temperature, 1 cup (200 g) light brown sugar, ½ cup (100 g) granulated sugar, ¼ cup (60 ml) maple syrup, 1¼ cup (325 g) canned pumpkin puree, 2 teaspoons (10 ml) vanilla extract
Bake for about 25 - 30 minutes or until the pumpkin bar cake bounces back with gently pressed. The edges of the pumpkin bars will also pull slightly away from the pan. Cool the bars in the pan to room temperature. Cool completely before frosting with the cream cheese icing. Make the cream cheese frosting for pumpkin bars by creaming the butter and cream cheese together until fluffy and well combined. About 2 - 3 minutes on medium-high speed. Add in the ground cinnamon, vanilla extract, salt, powdered sugar and 1 tablespoon milk. Cream all the ingredients on medium speed for 1 - 2 minutes. The frosting just needs to be fully creamed together.
8 oz. (226 g) cream cheese, room temperature, ½ cup (113 g) unsalted butter, room temperature, 2 teaspoons ground cinnamon , 2 teaspoons (10 ml) vanilla extract , ¼ teaspoon salt, 1 - 2 tablespoons (15 - 30 ml) milk, 4 cups (480 g) powdered sugar
Spread the cinnamon cream cheese frosting on top of the fully cooled pumpkin sheet cake bars. If the frosting is too warm or soft, place the frosted pumpkin bars in the fridge for 20 - 30 minutes. Slice and enjoy.