Cornmeal-Buttermilk Blueberry Biscuits

In a small baking pan, place the blueberries in one layer.
Freeze them for 30 to 45 minutes or until firm.
Set the oven at 400 degrees.
Have on hand a large, heavy baking sheet.
In a mixing bowl, sift the flour, baking powder, baking soda, cream of tartar, salt, and sugar.
Whisk in the cornmeal.
Scatter the chunks of butter over the mixture.
Using a pastry blender or two round-bladed table knives, cut the fat into the flour until it is reduced to the size of large peas.
Pour the buttermilk over the flour mixture, scatter over the blueberries, and use a spatula to stir lightly but thoroughly to form a dough.
Bring the dough clumps together with your fingertips.
The dough will be moderately moist but workable.
Turn the dough out onto a lightly floured counter.
With a rolling pin, roll it into a 3/4-inch-thick slab, keeping a square shape.
With a straight-edged chef's knife, cut the dough into 12 rectangles that are about 1 3/4-inches long.
Place them 1-inch apart on the baking sheet (if you prefer firmer sides), or 1/2-inch apart (for softer sides).
Bake the biscuits for 15 to 18 minutes, or until set and golden.
Transfer to a wire rack to cool slightly.