Wash, clean and slice the tomatoes. Wash nectarines, grate dry and cut into slices from the stone. Wash and clean the lettuce and drain well. Cut romaine lettuce into strips. Wash basil, dab dry and remove leaves. Pluck mozzarella into pieces. Arrange everything with Parma ham on a large plate.
For the vinaigrette, whisk vinegar, salt, pepper and sugar. Beat the oil in a thin stream. Drizzle some vinaigrette over the salad. Add the rest of the vinaigrette.