Preheat the oven to 350 degrees. Line a cupcake pan with 12 liners.
In a small bowl, whisk together the cake flour, baking powder, baking soda, salt and pumpkin pie spice.
1 ¼ cup (140 g) cake flour, spooned and leveled, ¾ teaspoon baking powder, ⅛ teaspoon baking soda, ¼ teaspoon salt, 2 teaspoon ground pumpkin pie spice
In a large bowl, cream together the softened butter and granulated white sugar with an electric mixer on high speed until fluffy, about 2 minutes.
5 tablespoon (70 g) unsalted butter, softened, ¾ cup (150 g) granulated white sugar
Add in the egg and vanilla and mix for 1-2 minutes on medium speed until pale in color and fluffy.
1 egg, room temperature, ½ teaspoon vanilla
Then mix in the canned pumpkin puree on low speed. Set aside.
½ cup (122 g) canned pumpkin puree
Add the dry ingredients and the buttermilk a little at a time to the wet ingredients. Mix until everything is combined.
¼ cup (60 ml) buttermilk
Fill each cupcake liner ¾ of the way full using a large cookie scoop.
Bake the cupcakes for 17-19 minutes, until a toothpick comes out clean from the centers. Let the cupcakes cool for 10 minutes in the pan, then trasfer them to a cooling rack to completely cool.