Prepare. Preheat your oven to 350°F. Prep your baking pan well for nonstick.
Dry Ingredients. In a medium bowl, use a whisk to combine together the baking powder, pumpkin pie spice, and salt.
Cream. In a large mixing bowl, beat together the softened butter and sugar on medium-high speed until pale and creamy (about two minutes).
Wet Ingredients. To the large mixing bowl, add the pumpkin puree, eggs and vanilla extract. Beat on a low-medium speed until well combined, scraping the sides of the bowl as needed. Then beat in the buttermilk.
Combine. Bump the speed down to low and gradually add the dry ingredients from the second step to the mixing bowl, mixing until just combined.
Transfer. Transfer the ingredients from the mixing bowl to your prepared pan. Gently tap the bottom of the pan on a countertop a couple of times and then place the pan into your oven.
Bake. Bake the cake for 25-30 minutes or until a toothpick comes out with just a few crumbs when inserted into the center of the cake.
Cool. Allow the cake to fully cool before adding the frosting.
Frosting. To make the frosting, simply combine together the ingredients until creamy and lump-free. You can make ingredient adjustments as needed to thin out the frosting or thicken it.