Boil the potatoes in salted water for about 15 minutes.
Slice the onion and radishes into thin slices.
When ready, cut the potatoes in half.
In a bowl, combine the olive oil, mustard, mayonnaise, lemon juice, salt, and pepper.
Toss the vegetables and add the chopped gherkins.
Use the sauce you prepared earlier and a seasoning.
Garnish with a little fresh parsley.