1. Place the leek, Celeriac, onion stock power, water and bay leaves in a oven proof pan with a lid put on the stove and bring to the simmer.
2. Heat oven to 140°c place the pan in the oven and cook for 2.5 – 3 hours
3. Remove from the oven remove the bay leaves and use a hand blender to blitz then season to taste with salt and pepper.
4. Serve in warm bowls with crumbled toasted walnuts and leek julienne and soya yogurt if desired.