Preheat the oven to 400ºF. In a mixing bowl, combine the flour and soda. Cut in shortening with a pastry blender or 2 knives until the mixture resembles coarse cornmeal. Add buttermilk. Stir until dough clings together. Turn the dough onto a lightly floured surface, knead lightly for about 15 seconds. Roll or pat the dough to 1/2 inch thickness. Cut into rounds with a 2 inch biscuit cutter. Place on a greased baking sheet. Brush tops with additional buttermilk, if desired. Bake for 12 minutes. Makes 24 - 30 biscuits