Put eggs in a pan of just simmering water and cook for 5-6 minutes for lightly cooked and 10 minutes for hard-boiled.
When cooked, drain and place in cold water until cooled. Carefully peel and leave in cold water until needed. Slice the potatoes; grill the Parma ham for 2 minutes, until crunchy.
To make a basic vinaigrette simply mix 3 tbsp of white wine vinegar with 150ml of vegetable oil. Add 1 tbsp of wholegrain mustard and whisk well to combine. Add the crushed garlic and seasoning.
Toss the watercress leaves with the dressing and potatoes. Place on a serving plate, cut the eggs in half and add to the salad, then crumble the cooked Parma ham over the top.
For the vinaigrette, add a pinch of dried chilli flakes for an extra kick or freshly chopped parsley for a fresh taste.