Scrape the potatoes and place in a saucepan. Cover with boiling water and cook for 12 minutes. Drain and allow to cool, then slice thickly. Peel and finely chop the onion. Peel the cucumber, slice lengthways and remove the centre seeds, then dice the cucumber flesh. Wash and shred the celery. Place all the vegetables together in a bowl and season well with salt and pepper.
Cut the hard-