Combine flour, baking powder, sugar, and salt; stir well. Cut in shortening until mixture resembles coarse meal. Add Sourdough Starter; stir until moistened. Turn dough out onto a lightly floured surface, and knead 10 to 12 times.
Shape dough into 1 1/2-inch balls, and place in a well-greased 13- x 9- x 2-inch baking pan. Brush tops of biscuits with melted butter. Cover and let rise 1 hour and 45 minutes or until doubled in bulk. Bake at 400° for 20 minutes or until golden brown.