Peel the celery and potatoes, cut into cubes and cook in the vegetable stock. Meanwhile fry the bacon cubes in a little butter, add the onion cubes and sauté until translucent.
Remove the celery and potatoes from the broth with a slotted spoon, drain a little and mash them in a bowl with the potato masher. Add the rest of the butter and enough milk to achieve the desired consistency. Mix the bacon and onion with the porridge and season with nutmeg, salt and pepper.
Sprinkle the celery and potato mash with the fried onions and serve.