Most folks know the Brennan family of restaurateurs in New Orleans as staunchly Irish, but at least one branch on the tree is Italian. Ralph Brennan, the proprietor of Brennan’s in the French quarter, has always held that his Italian mother made the best red sauce in all their generations of cooks. Here, Brennan shares a family holiday recipe that marries the tang of lemon and garlic with a Gulf Coast favorite—fresh head-on-shrimp.