There's a neon sign outside the Mi Tierra Restaurant in San Antonio's Market Square. It glows 24/7 in red defiance of the night. "We never close," it proclaims, proudly. That's not entirely true. The Cortez family has closed the 500-seat restaurant twice: for half a day on November 22, 1963 when John Kennedy was in town and another half day when patriarch Pete Cortez died. Other than those 24 hours, Mi Tierra has been in constant operation since 1951.