Spice and herb sachet: Bundle the bay leaf, thyme, black peppercorns and coriander seeds loosely in a small piece of cheesecloth to create a sachet. Tie with cooking twine to secure.

Cook onion and leek: Melt butter in large pot over medium-low heat. Add onion, leek, celery and garlic. Cook for 10 minutes until onion is soft but not golden. Don't rush this part – this creates an important flavour base so we can make this soup using water not stock.

Cook celeriac and potato: Add celeriac and potato. Cook for 10 minutes, stirring regularly, until the outside of the celeriac and potato starts to soften. Be careful to not colour the celeriac - we're going for a white soup here!

Simmer 25 minutes: Add salt, pepper, Spice and Herb Sachet, and water. Bring to a boil, then turn down to a simmer. Simmer for 25 minutes (no lid) until celeriac is very soft.

Cream: Add cream, simmer for another 3 minutes.

Blitz: Remove Sachet, then blitz until fully smooth using your method of choice: Stick blender (~ 3 mins), or cool slightly and do in a blender in batches (Note 5)

Adjust seasoning: Adjust salt and pepper to taste.

Serving: Ladle into bowls. Sprinkle with croutons and chives, drizzle with olive oil. Serve with crusty bread for dunking!