When the potatoes are completely cold, add them to a large bowl along with the mayonnaise, vinegar, parsley, chives, onion, gherkins, 1/4 tsp salt and pepper. Stir to combine.
50 g vegan mayonnaise, 1 tsp apple cider vinegar, 2 tbsp fresh parsley, 2 tbsp fresh chives, 50 g white onion, 50 g gherkins, 1/4 tsp pepper