1/2cupshredded cabbageSavoy or what ever is in season
Melt the butter with the oil in a pan over low heat. Add the onions, garlic and carrot. Cook gently until softened but not colored, about 10 minutes. Add the apples the celeriac and potato then the stock. Turn the heat to medium and bring to the boil. Season.
Simmer for 20 minutes. Cool for a while.
Put the soup in a food processor or use a hand held immersion blender and pulse until silky smooth.
Return the soup to a rinsed pan over medium heat, thin if necessary with water or stock. Reheat until simmering. Add the pancetta and cabbage and simmer until the cabbage is bright green about 15 minutes. Add salt and pepper to taste.