- 6 oz small boiling potatoes
- 1 1/4 teaspoons salt
- 1/4 cup fresh lemon juice
- 2 tablespoons drained bottled capers, rinsed and finely chopped, plus additional whole capers for sprinkling
- 1 1/2 teaspoons Dijon mustard
- 1 1/2 teaspoons sugar
- 1/2 cup extra-virgin olive oil
- 1 small red onion, halved lengthwise, then very thinly sliced crosswise
- 1 firm-ripe California avocado
- 1/2 seedless cucumber (usually plastic-wrapped), thinly sliced crosswise
- 3/4 lb thinly sliced smoked salmon
- 1/2 lb sliced pumpernickel bread, cut into triangles
- Peel potatoes and cut into 1/4-inch-thick slices, then transfer to a 2-quart saucepan and cover with water by 1 inch. Add 1/2 teaspoon salt and bring to a boil. Reduce heat and simmer, partially covered, until potatoes are tender, 5 to 8 minutes. Drain, then transfer to a bowl.
- Meanwhile, whisk together lemon juice, chopped capers, mustard, sugar, and remaining 3/4 teaspoon salt until sugar and salt are dissolved, then whisk in oil until emulsified.
- Toss potatoes gently with 1/4 cup dressing. Toss onion with 1/4 cup dressing in another bowl and let stand 5 minutes.
- Peel and pit avocado, then cut into 1/4-inch-thick slices.
- Arrange potatoes, avocado, cucumber, onion, salmon, and bread on a large platter and sprinkle with whole capers. Drizzle with some dressing and serve remainder on the side.