1. Place the chopped potatoes in a large pot and add the salt. Cover with water, about 2-3 cm above the potatoes. Heat over high heat until the water starts to boil and then lower over medium heat and cook until the potatoes are relatively easily pierced with a fork.
2. Store 1/4 cup of the pot water and then drain the potatoes and move them to a large bowl.
3. In a blender or food processor, add the olive oil, parsley, onions, lemon juice, mustard, garlic and pepper. Beat until the herbs and garlic have become small pieces. Then add the water you kept from the pot and stir the mixture again, until it has a milky texture.
— Tip: If you don’t have a food processor or blender, just finely chop the parsley and onions and beat all the ingredients together.
4. Pour the mixture over the potatoes and mix well. Let the potatoes aside for ten minutes.
5. Add the celery to the bowl, along with the chopped parsley and onions (2 tsp each). Stir the salad lightly and add salt and pepper, until it has the taste we want. Serve immediately or cover and place in the fridge, until it is time to serve.