Ask any Dane to name their favorite smørrebrød and the answer comes back with suspicious frequency. Not herring, not roast beef with remoulade, not shrimp piled on white toast. Kartoffelmad. Cold boiled potato on buttered rugbrød with crisp bacon, a drizzle of spiced mayonnaise, and a generous scatter of chives. Humble almost to the point of being a joke, and loved for exactly that reason.

The dish belongs to late summer and early autumn, when nye kartofler, the new Danish potatoes, are at their sweetest. You can make it year round and it will always be good, but in August and September, when the potatoes are small and waxy and still carry the taste of the soil they came from, kartoffelmad becomes something you remember. Boil the potatoes the night before, because they need to be cold and firm when you slice them. Warm potato goes to mush under the knife, and the architecture of this sandwich depends on slices thin enough to see through and whole enough to overlap.

Two things decide the dish: the potato and the bacon. Waxy potatoes, boiled gently so the skins don't crack, then cooled slowly in their own steam. Bacon cooked until it breaks cleanly between your fingers, not chewy, not burnt. The spiced mayonnaise pulls everything together with a soft curry warmth, and the chives give the green note that every good piece of smørrebrød needs. Each layer visible, each bite carrying all of them. You'll know when it's right.