In a large pot over medium heat, Melt butter with 1t truffle oil. Add potatoes, jerusalem artichokes. Stir to coat. Cook 10 mins. Add garlic. Stir well. Cook 5 mins or until garlic fragrant. Add unsalted water, stock. Bring to boil. Simmer about 30 mins or until potatoes & artichokes are tender. Remove from heat and puree with a hand blender or in a processor. Put soup back on low heat. Season. Add cream. Stir well. Cook 5 mins. Serve with a dash of truffle oil and some crusty white bread.