As a youth, he followed his dad around the backyard grill, learning techniques the old-fashioned way. As his infatuation — and independent studies — grew, so did his hobby: Keith opened Big Daddy BBQ food truck five years ago in the Northland area. “Brisket’s definitely our No. 1 sandwich,” Speed said, noting that Big Daddy’s sells 500 to 600 pounds a week during the busiest times. “First of all, we buy the best meat we can find,” Speed said. “That’s the key to it being tender.” The Big Daddy brisket sandwich ($12) offers a half-pound of beef served on a toasted sub bu...