In a small bowl, combine sour cream & ice water; set aside. In a large bowl, whisk together flour, cornmeal, sugar & salt. Using your fingertips, 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 liquid mixture, dough should be moist enough to stick together when pressed. Do NOT over work pastry. Press dough into a disk shape; wrap in plastic wrap & refrigerate until ready to use.