How to Make It
In a small saucepan, combine the diced potato with the truffle juice and bring to a boil. Cover and simmer over low heat until the potato is tender, about 20 minutes. Add the cream and return to a simmer.
Transfer the potato mixture to a blender. Add 3⁄4 teaspoon of salt and 1/3 cup of water and puree until smooth. With the machine on, drizzle in the truffle oil until incorporated. Season with salt. Strain the soup through a fine sieve into a medium bowl. Cover and refrigerate until thoroughly chilled, about 3 hours.
In a medium saucepan, melt the pound of butter. Simmer gently over low heat until foam rises to the surface, about 3 minutes. Using a spoon, skim the foam off the surface. Slowly pour the butter through a cheesecloth-lined sieve into a medium bowl, stopping before you reach the milky solids at the bottom of the saucepan; wipe out the pan. Return the clarified butter to the saucepan and add the potato balls. Bring to a slow simmer over moderately low heat and cook the potato balls until they are tender, about 15 minutes. Keep the potato balls in the butter.
Pour the chilled soup into 8 small bowls or shot glasses. Garnish each soup with 1 piece of cheese, frozen butter and chive, plus a hot potato ball and a truffle slice. Sprinkle with Maldon salt and serve. Alternatively, skewer 1 piece of cheese, frozen butter and chive and a hot potato ball onto each of 8 mini skewers, drape with a truffle slice, sprinkle with Maldon salt and serve.
Black truffle juice is available at Italian specialty stores and online at amazon.com.