4 tablespoons Sherry vinegar (available at specialty foods shops and some supermarkets)
3/4 cup olive oil
2 pounds boiling potatoes
4 large tomatoes (about 1 1/2 pounds)
1/2 pound mustard greens, stems and center ribs cut out and discarded and the leaves washed, spun dry, and shredded coarse (about 6 cups)
2 tablespoons minced fresh chives, or to taste
Directions
In a blender blend together the shallot, the mustard, the vinegar, and salt and pepper to taste, with the motor running add the oil in a stream, and blend the dressing until it is emulsified. The dressing may be made 2 days in advance and kept chilled in a tightly sealed jar.
In a large saucepan combine the potatoes with enough water to cover them by 1 inch and simmer them for 20 minutes, or until they are tender. Drain the potatoes, peel them, and let them cool. The potatoes may be prepared up to this point 1 day in advance and kept covered and chilled. Slice the potatoes 1/4 inch thick and arrange them decoratively on a platter with the tomatoes, cut into wedges, and the mustard greens. Pour the dressing over the salad and sprinkle the salad with the chives.
