Preheat oven to 350 degrees and line a cupcake tin with liners.
Mix together the flour, cocoa powder, baking powder, and salt. Set aside.
Beat the unsalted butter and oil together until combined and completley homogeneous - this will only happen if the butter is completely at room temperature. About 2-3 minutes on medium-high speed.
With the mixer on low, slowly add the granulated sugar, then turn it up to high and beat until light and fluffy. Then, with the mixer on low, add the eggs in, one at a time, scraping down the sides and mixing well in between each addition. Add the vanilla extract and mix on low until combined.
Add half of the dry ingredients and mix on low until combined. Add half of the buttermilk and mix on low until combined. Add the other half of the dry ingredients and mix until combined. Fold in the remaining buttermilk. Do not overmix!
Fill the baking cups ¾ of the way full and bake for 18-20 minutes. A toothpick or sharp knife should come out clean.