Bring a pan of salted water to the boil. Add the potatoes and boil for 20–25 minutes, or until tender to the point of a knife. Drain well and place in a bowl.
To make the mayonnaise, bring all the ingredients to room temperature and set a large bowl on a damp tea towel to prevent it from moving. Add the egg yolks, mustard and a pinch of salt to the bowl and mix wi