You can substitute additional butter for the shortening, if desired. The biscuits may not be quite as flaky if you do, but will taste just as good. The recipe also can be halved. Unbaked biscuits are freezable.
Preheat the oven to 450 degrees and place the rack in the middle position.
Combine the flour, sugar, baking powder, salt and baking soda in a large bowl and whisk together. (Ingredients 1-5 may be placed in a food processer and pulsed 4-5 times to mix.).
Add pieces of butter and shortening and, using a pastry blender or fork, cut into the dry ingredients until the pieces are about the size of small peas and evenly distributed. If using a food processor, pulse about 15 times, until the mixture resembles coarse meal.
Stir in the buttermilk, mixing with a spatula until the dough comes together in a rough ball. Turn the dough out onto a lightly floured surface and knead gently and briefly, no longer than 30 seconds, until the dough appears uniform. With a rolling pin, roll out the dough to about 1 inch thick. I allow the form to sit for about 5 minutes to allow the glutens to interact so cutting is easier.
Dip a 2 – 2 1/2-inch biscuit cutter in flour, then press straight down through the dough, without twisting (which makes the biscuit tough). Place the dough round upside-down on an ungreased baking sheet. Gather the scraps into another inch-thick piece and cut more rounds until all the dough is used.
Bake for 5 minutes, then reduce the heat to 400 degrees and bake for another 10 minutes, until golden brown. Serve immediately. Note: My picture is of one baked from frozen in a toaster oven.
Note: I prepare the dough then place the individual biscuits on a baking sheet covered with a sheet of wax paper then freeze. Afterwhich, I wrap the individual frozen biscuits in wax paper and place in a ziplock bag, squeezing out the excess air for later use. These may be baked frozen; increase baking time.