Speck or prosciutto: 3 slices， Juice of one lemon: ， Sunchokes, peeled: 2 pounds， Butter: 2 tablespoons， Olive oil: 2 tablespoons， Shallot, chopped: 1， Garlic, chopped: 2 cloves， Fresh thyme: 2， Chicken stock: 4 cups， Kosher salt and freshly ground black pepper: ， Truffle oil, for drizzling:
1Preheat the oven to 350 F.
2Line a baking sheet with aluminium foil and lay the speck on top. Lay a second sheet of foil on top, and then set a second baking sheet on top to ensure that the speck stays flat as it cooks. Bake for 10 to 15 mins. Remove and set aside until needed.
3Fill a large bowl with water and add the lemon juice. Cut any larger sunchokes so that all the pieces are of a uniform size and place them immediately into the bowl of acid ulster water so that they do not discolour.
4Heat a large saucepan over low to medium heat and add the butter and olive oil. When the butter has melted, add the shallot and garlic and cook gently until soft but not coloured. Add the thyme and stir. Drain the sunchokes and add them to the pan, stirring so that everything is evenly coated with the buttery mixture. Add the stock and bring to a boil, then reduce the heat to low and simmer gently until the sunchokes are soft - about 15 mins or so. Season with salt and pepper.
5Let the soup cool for a minute or so, then, using an immersion blender, blend until smooth. Take care not to splash yourself-the soup will still be extremely hot. Return to a gentle heat for a couple of minutes before pouring into serving bowls. Drizzle each portion with a little truffle oil and place a shard of the crisp speck on top.