Put the onion in a small, non-metallic bowl, and add the vinegar, sugar, a pinch of salt and 2 tbsp boiling water from the kettle. Cover and leave to pickle for at least 30 mins.

Cook the potatoes in a pan of boiling salted water for 15-20 mins until tender – a cutlery knife should be able to pierce them easily. Drain well. Heat the oven to 220C/200C fan/gas 7. Tip the potatoes into a roasting tray and press down using the oiled base of a glass, ramekin or spatula until the potatoes are squashed. Ensure the potatoes are in a single layer on the tray, then drizzle over the 4 tbsp olive oil and season. Roast for 20-25 mins until golden and crisp at the edges.

Drain the pickled onions, reserving the pickling liquid. Whisk the extra virgin olive oil, Dijon mustard and most of the dill into the reserved liquid. Tip the smashed potatoes onto a serving platter. Crumble over the feta and pour over the dressing. Scatter over the remaining dill and the pickled onions.