1. For dressing, stir together buttermilk, pesto and mayonnaise in small bowl. Toss together salad greens with 1/2 cup dressing in large bowl. Thinly slice reserved steak (from Pesto Steak with Croutons and Coleslaw on www.familycircle.com) across grain. Arrange on large serving platter with the dressed greens, reserved potatoes and tomatoes. Serve salad with extra dressing.