You might be wondering, what on Earth is a cardoon, anyway? A thistle-like plant, cardoons (also called cardone) grow abundantly in the Mediterranean and are usually in season from November to March. A close relative to the globe artichoke, the cardoon looks a bit like celery on steroids, growing as tall as six feet. It has thorny, silver-grey leaves and pom-pom-like purple blossoms.
It’s not exactly a friendly-looking vegetable and it probably won’t make you salivate at first sight. But their delicate artichoke-like flavor is as refined as it is addictive.
If you cannot find cardoons in your local store or farmers market, don’t despair! The velouté can be made with frozen artichoke hearts and tastes very similar.
*Note: You can replace the cardoons with frozen artichoke hearts. Use two 8-ounce packages of artichoke hearts and reduce the water to 2 ½ cups. Make the soup and strain exactly as for the cardoon soup.
**Note: You can find black truffle carpaccio in gourmet food supply stores or online.
Fill a large bowl with cold water and add ½ of the lemon juice.
Trim both ends of the cardoon stalks and all of the leaves. Using a paring knife, shave the edges off each stalk (they have little spikes on them), and peel off the large protruding ribs (as you would a celery stalk). Cut each stalk crosswise into 1-inch pieces and place immediately in the lemon-water bath.
Fill a large bowl with cold water and several ice cubes. Fill a large heavy-bottomed pot with water and bring to a boil over high heat. Add the remaining lemon juice and salt.
Drain the cardoon pieces and add them to the boiling water. Boil until just tender, but still a bit firm, about 15-20 minutes. Scoop them out with a slotted spoon and transfer to the ice water bath until cool. Drain on kitchen towels or paper towels.
Heat a large, heavy-bottomed soup pot over medium-high heat. Add the olive oil and onion, stir well, and sauté until just golden, stirring occasionally, about 5-6 minutes.
Add the wine and garlic. Stir well and continue to sauté until the wine has reduced to a syrupy sauce and has almost all evaporated, about 2-3 minutes. Add the cardoons, potato, stock, and water. Season with salt and pepper, to taste.
Tie the parsley and thyme together in a bundle with kitchen string and add to the pot. Bring to a boil, then reduce heat to medium-low, cover the pot, and simmer for 40 minutes until the cardoons are very tender. Remove the herb bundle and discard.
Purée the soup with a stick blender or food processor until very smooth. Pour some of the soup in a medium sieve, 2/3 of the way up. Force the soup through the sieve with a silicone spatula. When there is nothing left but a thick paste, discard the paste and pour another batch of soup in the sieve. Repeat until the entire soup has been strained.
Return to the soup pot and gently reheat over medium heat. Add the crème fraîche and stir until well incorporated. Season with additional salt and pepper, if needed.
Ladle the soup into soup bowls, put a spoonful of black truffle carpaccio (or a spoonful of truffle oil) in the center of each bowl, garnish with the chives and serve immediately.