In a large bowl, whisk together the flour, sugar, baking powder, and salt. Make sure there are no large clumps of flour and that the leavening agents are spread out evenly.
Add the frozen butter cubes to the flour mixture. Use a pastry cutter or two knives to chop the butter into the flour until the pieces are about the size of peas. You aren’t looking for a smooth paste; you want to see visible chunks of butter covered in flour.
If you use your hands, try to work quickly so the heat from your fingers doesn’t soften the butter.
Add the fresh blueberries to the flour and butter mixture. Gently toss them around with a spoon so each berry is coated in a thin layer of flour. If you are using frozen berries, do not thaw them first.
Turn the dough out onto a lightly floured surface. Gently pat it into a rectangle and fold it in half. Turn it ninety degrees, pat it down again, and fold it in half once more. Repeat this folding process about four or five times. Be careful not to crush the blueberries while you are folding the dough.
Pat the dough down until it is about an inch thick. Use a circular biscuit cutter to press straight down into the dough. If you don’t have a cutter, you can use the rim of a glass or even just cut the dough into squares with a sharp knife. Place the biscuits on a parchment-lined baking sheet so they are just barely touching each other.
Slide the tray into an oven preheated to 425°F. Bake for 15 to 18 minutes until the tops are a beautiful golden brown and the blueberries have started to burst.
