In a small bowl, combine sour cream & ice water; set aside. In a large bowl, whisk together flour, 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 the dough, 1 Tbsp at a time, tossing with a fork to evenly distribute it. After you have added all the sour cream, dough should be moist enough to stick together when pressed; if not, add additional cold water, 1 tsp at a time. Do not overwork dough.