Heat the oven to 180°C, Gas 4. Put the celeriac on a roasting tray, drizzle 2 tbsp olive oil and sprinkle the sage over and season well. Roast for 30 minutes.
Step 2
Meanwhile, heat the remaining oil in a large heavy bottomed pan over a medium heat. Add the the onion and cook for 2 minutes. Add the garlic and cook for a further minute. Add the bay leaf, potato, stock, cream and the cheddar. Bring to the boil and simmer for 15 minutes.
Step 3
Add the roasted celeriac and simmer for a further 5 minutes. Blitz with a blender and serve.