For the soup
Place a pot over medium heat. Add the butter, olive oil, onion, leek and bacon, season with salt and sauté until softened. Add thyme and stir for around 1 minute. Add the potato and stock, bring to the boil and then reduce heat. Season with salt and simmer until ingredients are soft. Season with salt to taste, add the cream and cook for a further 10 minutes. Mix well in a blender and pass through a fine sieve. Taste for seasoning. If not planning to use immediately, cool rapidly and store in the fridge.