Add the flour, baking powder, salt, baking soda, and butter to the bowl of a food processor. Cover and pulse until the mixture resembles coarse meal.
Pour the flour mixture into a large mixing bowl and add the buttermilk. Stir until just combined. (Don't overmix!) The dough should be very sticky. If it's dry, add more buttermilk 1 tablespoon at a time.
Dust your counter with flour and turn out the dough onto the work surface. Sprinkle more flour on top of the dough, and use your hands to form it into a circle. Then flatten it down to a ½-inch thickness.
Using a biscuit cutter, cut out biscuits and place them in a cast-iron skillet or round baking pan. Rework the dough scraps into a ½-inch thick circle and cut out more biscuits until all the dough has been used. (You should get about 12 biscuits.)
Bake for 13-16 minutes or until golden brown on top. Remove the biscuits from the oven and transfer to a wire rack to cool slightly.
Notes
If you don't have a food processor available, add the flour, baking powder, baking soda, and salt to a large mixing bowl. Stir that together and then add the butter pieces. Use a fork or pastry cutter to cut the butter into the dry ingredients until it resembles coarse meal. Then, pour the buttermilk into the same bowl and continue the recipe.