In Italy, this potato salad is known as Russian Salad. It has a thousand versions, most of them bound with plain or garlic mayonnaise. In this one, lightly steamed vegetables are splashed with vinegar while still hot, so they absorb the pungent aroma and flavor. A lemony vinaigrette binds the vegetables together. This salad looks especially pretty when made with red-skinned new potatoes and served in a cupped leaf of red radicchio. Butter lettuce or ruffled kale makes a nice presentation too.