Preheat oven to 450 degrees.
In a large bowl, combine flour, sugar, baking powder, salt and baking soda.
Slice butter and cut into flour mixture with a pastry cutter or fork.
Add the sourdough starter and buttermilk. Stir until a soft dough forms.
Working on a lightly floured surface, knead the dough 2-3 times until it comes together. Using a rolling pin, roll the dough into a 1 1/2-inch thick rectangle. Cut out biscuits using a 2-inch biscuit or cookie cutter.
Place biscuits on baking sheets. Place into oven and bake for 15 minutes or until golden brown.
Serve warm with gravy or with butter and jam.
