Peel and wash the potatoes and cut them into halves or quarters depending on their size. Cook in boiling salted water for about 20 minutes. Clean, wash and cut spring onions into rings. Pour the gherkins into a sieve and drain.
Cut the gherkins into slices. Cut cheese into cubes of about 1 cm. Wash apples, quarter them, remove seeds and cut into quarters. Cut quarters into fine slices.
For the salad dressing, mix mustard, 6 tablespoons vinegar, 1 tablespoon sugar, salt and pepper. Fold in the oil. Season to taste with salt and pepper. Mix with spring onions and apple wedges. Drain the potatoes and let them drain well.
Pour 4 tablespoons of vinegar over it and toss in a closed pot. Let the potatoes cool down for about 30 minutes. Cut ham slices into wide strips. Mix everything and arrange.