Preparation Whisk first 4 ingredients in small bowl to blend. Gradually whisk in olive oil. Season dressing with salt and pepper. Steam russets until tender, about 8 minutes. Transfer to large bowl; toss with 1 tablespoon dressing. Steam yams until tender, about 7 minutes. Transfer to medium bowl; toss with 1 tablespoon dressing. Fry bacon in large skillet until crisp. Transfer to paper towels. Drain. Crumble bacon. Add yams, bacon and mustard greens to russets. Toss salad with enough dressing to coat. Season with salt and pepper. (Can be made 2 hours ahead. Cover and let stand at room temperature.)