Bring salted water to a boil in a saucepan. In the meantime, peel the celery, cut into ½ cm thick slices and cook them for approx. 15 minutes, not too soft. He should still have some bite.
Peel and finely chop the onion and place in a large bowl. Then add the remaining ingredients for the dressing and beat well with a whisk.
Drain the celery and stir into the dressing while still warm and carefully stir in. Then let it sit for about 1 hour. Season again to taste before serving.