Creamy, cold, and made ahead, northern German potato salad is the style most people outside Germany picture when they hear the name. Bound with mayonnaise and enriched with hard-boiled eggs, gherkin, and onion, it is generous, satisfying, and best when it has had time, at least a few hours, ideally overnight, to let the flavours come together. It is the standard accompaniment at northern German barbecues, birthday parties, and Christmas Eve dinners, and it is the potato salad you want alongside a large piece of grilled meat.