In a large saucepan heat the butter and the oil until the butter has melted

Add the leeks and sauté until soft

Roughly cut the florets off the cauliflower, keeping the stems on

Add to the pan and give them a good stir

Add the stock and season generously

Bring to the boil, reduce the heat, cover and simmer for 30 minutes

Using a stick blender, puree the soup and then adjust the seasoning

Serve with a few drops of truffle oil and a generous shaving of Parmesan cheese