Preheat the oven to 375 degrees.In a large bowl mix together the flour (or biscuit mix) and sour cream with a pastry blender. Add the Sprite a little at a time, mixing with a fork until the dough forms a ball. Cover your work surface with the additional flour and turn out your dough onto the counter. Sprinkle your hands with flour and work the dough into a circular disc adding more flour as necessary. With a rolling pin, roll the dough to ½ inch thick. Using a round biscuit cutter, cut out the biscuits- dipping the cutter into the flour before each cut.Melt the butter in a 12 inch cast iron skillet.Dip each biscuit in the melted butter and place the biscuits close together in the skillet. Bake for 20 minutes, or until the tops are golden brown.