Method

• 1.
  Preheat oven to 200°C. Parboil potatoes until just soft, then drain. When cool enough to handle, break potatoes up and toss in 1 tablespoon of oil. Season with salt and pepper. Place on a roasting tray and cook for 25-30 minutes, turning occasionally to ensure they brown evenly, until crisp and golden.
• 2.
  Whisk together the remaining olive oil, sherry vinegar and lemon juice, and season with salt and pepper.
• 3.
  To serve, toss the warm potatoes with the watercress and vinaigrette.