Preheat oven to 350°F. Oil a 9x13-inch pan and line the bottom with parchment paper; set aside. In a medium bowl, mix together whole wheat pastry flour, baking powder, salt, and spices; set aside.
In a large bowl, mix together butter and sugars until light and fluffy. Add eggs and vanilla and scrape down the bowl as needed. Add pumpkin puree and sour cream and mix well. Blend in dry ingredients until just incorporated.
Pour batter into prepared pan and spread evenly. Tap the pan lightly to work out any air bubbles. Bake until a toothpick inserted into the center comes out clean, 30 – 35 minutes. Let cool completely before frosting.
In a large bowl, mix softened cream cheese and butter until well combined. Add powdered sugar and mix until light and fluffy, about 3 – 5 minutes.
Remove bars from pan and remove parchment paper. Frost with cream cheese frosting then cut into 2x3-inch bars or into the desired size and shape.