Peel and parboil the vegetables. When they are cool enough to handle, shred them on a grater or in the food processor. Mix together, and season with the salt and pepper.
Melt half the butter in a small frying pan, and press the vegetable mixture into it. When cooked and brown on one side, slide it on to a plate. Melt the rest of the butter, and cook the celeriac cake on the other side u