Kartoffelsalat

Boil the potatoes in their skins in water salted with 1 tbsp of the salt for 20 to 25 minutes, until a knife meets only slight resistance in the centre. Take them out a shade early rather than late; potatoes that have gone floury collapse into the dressing.

While the potatoes cook, finely chop the onion and bring the stock to the boil with it, the vinegar, the mustard, the sugar, the remaining salt and a good grind of black pepper, and simmer for 2 minutes so the onion loses its raw bite.

Drain the potatoes and let them steam dry for 2 minutes, then peel them while they are still too hot to hold comfortably, gripping each one in a tea towel.

Slice the warm potatoes about 5 mm thick straight into a wide bowl. Warm slices drink the dressing in; cold ones sit in it.

Bring the dressing back to the boil, pour it over the potatoes and turn them gently with a flat spoon. It will look far too wet at this point, which is right.

Leave to stand at room temperature for 30 minutes, turning once more halfway through. The liquid disappears into the slices and the salad turns creamy on its own.

Snip the chives. Fold through the oil and most of the chives, then taste and add a little more salt or vinegar if needed. Scatter the rest of the chives over. Serve warm or at room temperature, never straight from the fridge.