Preheat oven to 375°F. Line a baking sheet with aluminium foil. Place bacon on baking sheet and roast until crispy, about 8 minutes. Remove from pan and allow to cool slightly. Crumble into small pieces and set aside.
Meanwhile, in a large saucepan over medium heat, combine sunchokes, vegetable stock and salt, ensuring there is enough liquid to cover the sunchokes. Cook until sunchokes are tender, about 15 minutes. Purée the soup in batches using a blender or food processor, or in the saucepan with an immersion blender. Return to saucepan and add cream and butter. Cook over medium heat until heated through. Season with salt and pepper to taste. To serve, spoon the hot soup into bowls and top with bits of bacon.