- 2 pound Yukon Gold potatoes
- 3 tablespoons cider vinegar
- 3 tablespoons grainy mustard
- 2 1/2 teaspoons sugar
- 1/3 cup olive oil
- 1/2 pound smoked mackerel, skin discarded and fish flaked into 1/2-inch-wide pieces
- 4 scallions, chopped (1 cup)
- 1/3 cup chopped dill
- Cut potatoes into 1 1/2-inch pieces and cover with cold water in a large pot. Add 1 1/2 teaspoons salt and simmer over medium heat, partially covered, until just tender, 12 to 15 minutes.
- While potatoes cook, whisk together vinegar, mustard, sugar, and 1/4 teaspoon salt in a large bowl until sugar and salt are dissolved. Add oil in a slow stream, whisking until combined.
- Drain potatoes well and, while still hot, stir into dressing to coat, then stir in mackerel, scallions, and dill. Serve warm or at room temperature.