In a world where restaurants shutter after a fortnight and "historic" is laughably used to mean "established in 1988", it's nice to see a genuine icon (yes, nosh counts!) making it to 75. Maybe it's the formula--pure comfort food that's virtually unchanged since day one, way back in 1934, when Walter Knott convinced his wife Cordelia to add more items to her modest tea room menu.A legend was born: country-fried chicken, mash and gravy, salad (for health!), corn or cabbage with ham, all-you-can-e