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 the butter until mixture resembles BOTH coarse crumbs & small peas. Sprinkle the cold sour cream mixture over dough, 1 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 ice water, 1 tsp at a time. Do NOT over work the pastry.