Wash the potatoes with their skins on and boil for 30–35 minutes until tender. Drain, peel, cut into pieces, and place in a salad bowl.

Add the onion and drained capers.

Whisk together the mayonnaise, mustard, heavy cream, and olive oil until smooth.

Season the potatoes with salt and pepper, then pour the cold dressing over them while they are still warm.

Gently toss, sprinkle with parsley, and serve.