1. Boil sliced potato in salt water until tender (5-6 mins)
2. For the dressing, add 1/2 cup parsley, 1/2 onion, 2 garlic cloves, two teaspoons Dijon mustard, juice of half a lemon, two tablespoons olive oil + water from the boiled potato. Mix all in a food processor
3. Add to a large bowl the potatoes, parsley, 3 celery sticks, and 1/2 cucumber