Combine first 5 ingredients in a nonmetal bowl; mix well. Cut in 2 tablespoons shortening until mixture resembles coarse meal. Add Sourdough Starter, stirring until moistened. Turn dough out onto a lightly floured surface, and knead lightly 3 or 4 times.
Roll dough out to 1/2-inch thickness; cut with a 2 1/2-inch biscuit cutter. Place biscuits in 3 lightly greased 9-inch square baking pans, and brush tops with melted butter. Cover, and let rise in a warm place (85°), free from drafts, 45 minutes or until doubled in bulk. Bake at 450° for 10 to 12 minutes or until lightly browned.