Grease a baking pan.
In a large bowl, sift together flour, sugar, baking powder, baking soda, and salt. With a pastry blender or two knives, cut in butter or margarine until particles are the size of small peas. Mix in sourdough starter. Sprinkle in water, 1 tablespoon at a time, tossing with fork until all flour is moistened and pastry dough almost cleans side of bowl (1 to 2 teaspoons additional water can be added if necessary). NOTE: You want the ingredients to barely bind together.
On a lightly floured surface, knead dough gently a few times until dough forms a cohesive mass.
Gently roll dough to approximately 1/2-inch thickness. Cut with a floured 2-inch biscuit cutter and place onto prepared baking pan. Place close together for soft-sided biscuits or 1-inch apart for crisp-sided ones. Brush with butter. Cover and let rise in a warm place (85 degrees F.), free from drafts, about 1 hour.
Preheat oven to 425 degrees F.
Bake 15 to 20 minutes or until tops are a light golden brown. Remove from oven and immediately remove from baking sheet. Serve warm.
Makes 10 biscuits.
* The thickness of your sourdough starter can determine how much flour needs to be used. If you think the dough is too moist, add additional flour (a tablespoon at a time). The same is true if the dough is looking dry and gnarly - add additional warm water (a tablespoon at a time).
** If you do not presently have a sourdough starter, either make your own sourdough starter or purchase packaged Sourdough Starter Mix by mail-order.
Sourdough Biscuits Recipe: https://whatscookingamerica.net/Bread/SourdoughBiscuits.htm