In a large bowl, whisk together the dry ingredients; all-purpose flour, baking powder and baking soda, sugar, and salt. Add in a cold stick of butter that has been cut into cubes. Toss to coat with flour mixture.
You should end up with small pieces of butter incorporated into flour with the texture of lumpy sand. Add in your blueberries and toss to coat in the flour.
Make a well in the center of the mixture and add the cold buttermilk. Use a rubber spatula or wooden spoon bring everything together until you have a fairly uniform dough.
If there are a lot of dry spots, add one or two tablespoons more buttermilk. Dump the dough out onto a floured work surface.