Preheat the oven to 425 degrees F or 218 C. Prepare two doughnut pans with nonstick cooking spray.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a mixing bowl, beat the butter, oil, brown sugar, and sugar until well blended. Scrape down the sides. To the batter, add the eggs and vanilla and mix well.
Add the flour mixture about ⅓ at a time, alternating with the buttermilk. Beat just until blended.
In batches, transfer the batter to a piping bag and pipe in circles into the prepared doughnut pans, filling them about two-thirds full.
Bake for 8-10 minutes.
Allow the doughnuts to cool in the pans for 5 minutes on a wire rack before removing them from the pans. Allow the doughnuts to cool completely prior to decorating.
For the cocoa powdered doughnuts, place the powdered sugar and cocoa into a gallon-sized zip top bag. Seal the bag and shake to combine.
Add the doughnuts about 4 at a time, sealing the bag, and turning until the doughnuts are coated.
Store in an airtight container.