Heat 1 tbsp oil in a large, heavy based saucepan. Gently fry a chopped leek until soft. Add 1 tsp ground cumin and stir.
Add the chopped celeriac, 2 chopped parsnips and 3 chopped carrots and cook for five minutes, stirring frequently, until the vegetables are coated in the cumin leek mixture.
Add 1 litre of vegetable stock and bring to the boil. Reduce the heat to a simmer, cover with a lid and cook over a low heat until all the vegetables are soft. Use more stock (or add water) for a thinner soup. Season to taste with salt and pepper.
Blend until smooth. If using a jug blender allow to cool a little first.
Serve with crusty bread, freshly chopped parsley, caraway seeds or your favourite soup toppings.