Method

• 1.
  Place the potatoes and the mint sprig in a saucepan of well-salted water (use 1 teaspoon salt per 600ml water). Bring to the boil over high heat, then boil for 15-20 minutes until the potatoes are tender. Drain well, then return the potatoes to the saucepan off the heat. Add the oil, then gently crush each potato against the side of the saucepan with the back of a fork until it just bursts open.

• 2.
  Season well with sea salt flakes and freshly ground black pepper, then add the watercress. Turn the potatoes and watercress over gently until combined. Transfer to a platter, then serve straight away with the chargrilled beef.