Whisk together the flour, baking soda, baking powder and salt in a bowl.
Add the very cold butter cubes into the flour mixture and, using a fork or a pastry cutter, cut the butter into the flour until you have a grainy mix with some pea-sized pieces of butter still in it.
Add the sourdough starter, a little at a time, mixing with the fork until you have a dough that just holds together. Don't get the dough too moist, but it should be able to ball up, with little bits of butter visible throughout. You may not need all of the starter, depending on the hydration of your starter, or you might need a little more than a cup.
Dump the dough into a square of cling wrap and wrap tightly, using your palms over the cling wrap to shape the dough into a disc. At this point you can refrigerate for either 15 minutes or, for the best results, overnight.
Remove the cling wrap and roll out the dough on a lightly floured surface to 3/4ths inch thickness.
Preheat the oven to 425 degrees F
Use a round or square cookie cutter to cut out biscuits. After cutting biscuits, push the dough together to form a rectangle, roll again to 3/4th inch thickness, and cut more biscuits. Repeat until all the dough is gone.I used a 2-inch cookie cutter, which gave me 12 biscuits. A larger cookie cutter will yield fewer cookies.
Place the biscuits on a baking sheet, two inches apart. Bake 23 minutes or until golden brown on top and bottom.
Place the biscuits on a rack. Serve warm.