In a large soup pot, cook diced celery and onion with a drizzle of olive oil for 5 minutes until softened, then add the stock.

Heat the stock through, then incorporate two-thirds of both the chopped potato and grated cheese, along with all the heavy cream and sour cream, stirring to combine.

Carefully puree the soup until smooth using a blender or immersion blender, then return it to the pot and stir in the remaining chopped potatoes and most of the scallions; simmer for 5 minutes, then taste and season with salt and pepper.

Garnish individual servings with the remaining cheese and scallions before serving.