Peel the root vegetables and cut them into small pieces.
Put the root vegetables in a saucepan. Pour water over until just covered. Bring the pot to a boil and let the root vegetables cook under a lid for approx. 15 minutes. Prick them to check if they are tender.
Pour off the water and save it for later.
Mash the root vegetables with a fork or a mashed potato.
Add the fat.
Add a little of the stored vegetable water until the bog has a suitable thickness.
Check that it has the correct eating temperature before giving it to the child.