Melt the butter in a pot. Add the celery, bay leaf, leek, thyme and onion. Season well and sweat without colouring until the onions soften. Add the stock cubes and mix until they dissolve. Now add the flour and mix well.

Turn the heat down low and cook, stirring every 20 seconds, for four to five minutes. Add the chicken stock (or water). Mix well and leave to come to the boil. Once boiling, turn down to a simmer for 35-40 minutes.

While the soup is simmering add the pancetta to a cold, heavy-based, non-stick pan. Sauté on a low heat until all the fat has rendered and the pancetta becomes crispy. Spoon it onto kitchen paper to remove excess fat.

Remove the bay leaves and fresh thyme then blend the soup into a purée with a stick blender. Add the cream until it’s at the desired consistency. You may need a little more or a little less, depending on your own preference. Mix in the truffle oil. Season with the salt and white pepper.

Butter each side of the sourdough slices and pan fry until golden. Divide the grated cheese between the slices and leave to melt slightly. Serve the soup topped with the pancetta and with the sourdough on the side. If you have fresh truffle, add a decent shaving to each bowl before serving.