Peel, and cut potatoes in 4 and cook potatoes in large pot of boiling salted water.  The heat must not be to high, as you want the potatoes to cook through. Drain and transfer potatoes to a large bowl.

Drizzle vinegar over hot potatoes. Cool at room temperature.

Chopped hard boil eggs and picked cucumber.

Add eggs, pickled cucumber and onions to the potatoes.  Flavor to taste with salt and pepper.

Whisk mayonnaise, sour cream and mustard.

Pour over potatoes. Cover and refrigerate.