Step #1 Put the freshly sliced celery root as soon as possible into the stock which should be flavored with 1 tbsp each oil & vinegar, 1/2 tsp salt, the sugar, & the sliced onion.
Step #2 Cook for about 20 mins - until the celery root is quite tender & the liquid has almost boiled away.
Step #3 Spice up the celery root & beef stock with the remaining oil & a dash or two of wine vinegar, as well as with salt if you wish.
Step #4 Note: If the salad is to be served as an appetizer, mix in some coarsely sliced walnut & garnish with a few walnut halves.
Step #5 Nowadays, it may be more usual to substitute grated uncooked celery root, in this age of crudites, marinated in oil & vinegar, and possibly mixed with grated raw carrot.