In these biscuits, dark pools of blueberry lend a concentrated flavor to the pleasingly gritty interior. They rise beautifully and turn golden in the oven, announcing that berry season is in full swing.
The biscuits are made with baking powder, baking soda, cream of tartar, plenty of butter, buttermilk, and only a little sugar. Mix them the old-fashioned way: in a bowl with a pastry blender or two blunt knives. To keep the berries from turning pulpy in the dough, freeze them for half an hour until they are firm and marblelike. Stir them in, and then work quickly to bring the dough together. Roll it into a thick slab and with a straight-edged chef's knife, cut out rectangles.
