Bring the potatoes to the boil in salted water and then turn down to a simmer. When cooked, drain and allow to steam for a couple of minutes before lightly crushing with a fork.
Finely slice the spring onions. Juice the lemon. Fry the bacon lardons until crispy and then drain onto a piece of kitchen paper to remove any unwanted fat. Add all these ingredients to the potatoes with the remaining olive oil. Check the seasoning.
Whisk together the sherry vinegar and the mustard. Slowly pour in the olive oil and walnut oil to emulsify the dressing. Season with black pepper.
Pick and wash the watercress. Dry in a salad spinner. Dress with the sherry vinegar and mustard dressing.
Place the crushed potatoes on the plate with a stainless steel ring, put the chicken next to it and finish with a neat pile of watercress salad. Serve with a wedge of lemon.
«This potato salad can easily be turned into potato cakes. Omit the lemon juice and then make the mixture into patties. Pan fry until golden brown and serve alongside any meat or white fish.»