Halve pumpkin and scoop out the seeds. Clean and roast with olive oil and salt (and a little grated truf-fle), and nibble while confecting the soup (or serve alongside). Bake pumpkin halves upside-down until soft, then scoop out the insides. Throw in a soup pot, along with cubed potatoes and broth, and cook until potatoes are tender. Purée the mixture with an immersion blender, season, and add grated truffle. Ladle into soup bowls, pouring in a teaspoon of heavy cream or topping with a sliver of butter, fan out with a knife, and finish with more grated or thinly-slivered truffle.