Pulse the flours, baking powder, baking soda, sugar, and salt in the work bowl of a food processor to combine. Add cubed butter and process for 12 1-second pulses. Add the buttermilk and process until the dough comes together in moist clumps, about eight 1-second pulses.
Transfer the dough to a lightly floured work surface and shape into a rough ball, being careful not to overmix or handle too much. Cut the dough into quarters then divide each quarter into thirds. Quickly and gently shape each dough piece into a rough ball and place on an ungreased baking sheet. Make ahead: wrap the baking sheet in plastic wrap and refrigerate for up to 2 hours before baking.
Bake until light brown, about 10 to 12 minutes. Serve immediately.
Notes
If you don't have a food processor, you can use two knives or a pastry blender to cut the butter into the flour mixture.From The New Best Recipe