Long before Derrick Walker knew how to cook barbecue, he learned to make soul food with his grandmothers. “My grandma would pull up a stool next to the stove and let me watch everything,” Walker said, referring to his mom’s mother. “Eventually she started letting me do it.” He remembers watching old westerns on the television while both grandmothers patiently showed him how to make things like smothered pork chops, candied yams, and fried chicken. Walker was a quick study. “I was probably twelve when I took over the cooking at home,” he said. That included getting his older brother, who Walker said “couldn’t boil water,” to do Walker’s chores in exchange for freshly fried chicken.Walker has run Smoke-A-Holics BBQ, in Fort Worth, with his…