Peel or clean, wash and chop the vegetables. Peel and finely chop onion and garlic. Wash thyme, shake dry, remove leaves. Bring 3-4 l salt water (1 teaspoon salt per litre) to the boil.
Peel and finely chop the onion. Mix vinegar, 2 tablespoons of water, salt, pepper, sugar and diced onion and add the oil. Peel and finely dice the eggs and add to the vinaigrette. Arrange watercress, melon and Parma ham on plates and cover with the vinaigrette.
Baguette tastes good with it.