It's a chef's quiet confession: Even the most celebrated cooks sometimes crave a drive-thru treat. For celebrity chef Aarón Sánchez, the indulgence of choice is Whataburger - and not because of nostalgia alone. The Texas-born chain builds its burgers with mustard as the only condiment cozied up beside diced onions, pickles, lettuce, and tomato, and for Sánchez to claim it as his favorite fast food restaurant burger is quite the endorsement.