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 fingertips, cut in butter until mixture resembles BOTH coarse crumbs & small peas. Sprinkle the cold sour cream mixture over dough, I Tbsp at a time, tossing with a fork to evenly distribute it. After you have added all the sour cream mixture, 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.