How to Make It
In a small bowl, toss the sliced onion with the vinegar to coat. In a medium saucepan, combine the potatoes with the bay leaf and 1 tablespoon of salt, cover with 1 inch of cold water and bring to a boil. Cook over moderate heat until the potatoes are fork-tender, about 12 minutes. Drain the potatoes, return them to the saucepan and toss with a generous pinch of pepper and 1 tablespoon of the olive oil.
Spoon the potatoes onto 4 plates and arrange the smoked salmon over them. Drain the onion slices and return them to the bowl. Add the capers, lemon juice and the remaining 1 tablespoon of olive oil and spoon the onion mixture over the smoked salmon. Add the crème fraîche to the bowl, stir once or twice and then drizzle it over all. Scatter the chervil and chives on top and serve.