Peel the potatoes, carrots, and celery root.
Boil the peeled potatoes, carrots, and celery root whole in salted water until they are tender. Add the peas during the last 2-3 minutes of cooking. Drain thoroughly and let everything cool completely.
Once cooled, carefully cut the boiled vegetables into small, even cubes.
Boil the eggs until they are hard-boiled. Let them cool, then peel and dice them finely.
Peel the pickles, chop them finely, and squeeze out all excess liquid to prevent the salad from becoming watery.
Ensure your white onion is very finely diced, as specified.