In a small bowl, combine sour cream & ice water; set aside. In a large bowl, whisk together flour, 1/2 cup cornmeal, sugar & salt. Using a pastry blender or finger tips, cut in butter until mixture resembles both coarse crumbs & small peas. Sprinkle the cold sour cream mixture over dough, tossing with a fork to evenly distribute it. Do NOT overwork dough.