Boil potatoes in salted water for 20-25 minutes.
Drain & peel. Let the potatoes rest for about 10 minutes.
Peel & dice onions.
Heat the onions, broth, vinegar, sugar, salt, and pepper to a skillet. Simmer 10-12 minutes.
Remove from the stovetop and whisk in the oil.
Cut the potatoes into slices.
Slice the gherkins.
Peel the cucumber.Halve lengthwise & deseed.
Halve the cucumber lengthways again and cut into quarters.
Finely chop the chives.
Toss the potatoes, cucumbers, chives, gherkins, and vinaigrette together in a bowl & serve