Peel the apples, remove the cores and cut into pieces. Peel the celeriac and cut into pieces too. Heat the vegetable stock.
Put the potatoes, apples and the celeriac together in a pan. Add salt and pepper and pour over 500 ml vegetable stock. Put on medium high fire with the lid on for about 20-30 min or till everything is soft enough to blend together.
Using a stick blender to puree the soup while adding the almond milk. Use the additional 250 ml of stock if the soup is too thick.