Preheat the oven to 400 F/ 200 C/ gas mark 6. Line a medium size baking sheet with parchment and set aside.To prepare the celeriac cut the knobs off then simply peel the celeriac using a vegetable peeler.
Cube then arrange the celeriac on top of a baking sheet, brush with the oil and season lightly. Roast in the centre of the oven for 25 minutes, until lightly browned and tender. Stir half way through.
Remove from the oven, combine with the rest of the ingredients and puree until the mixture is smooth. Season to taste and serve.
You can either use a food processor or high speed blender to puree the celeriac (if you want a super smooth finish use a blender).
Adjust the amount of milk and/or yogurt to suit your preference.
Best served immediately.
Keep refrigerated, covered, up to 3 days. The puree will thicken as it cools so you may want to add a drop of milk when reheating it.
Freeze for up to 3 months.
See the post for serving suggestions and substitutions.