How to Make It
Squeeze the lemon juice into a bowl of cold water and add the lemon halves. Using a sharp knife, halve the artichokes crosswise. Discard the tops. Working with 1 artichoke at a time, pull off all the outer green leaves until you reach the tender yellow leaves. Trim off the dark green skin. Scrape out the hairy choke with a teaspoon, then quarter the heart and drop it into the lemon water.
Peel and coarsely chop the sunchokes. Add them to the artichokes in the lemon water.
In a large enameled cast-iron casserole, heat the olive oil. Add the pancetta, onion, carrot, celery and garlic and cook over high heat, stirring occasionally, until softened, 5 to 6 minutes. Drain the artichokes and sunchokes and add them to the casserole along with the marjoram and thyme and cook, stirring, for 3 minutes. Add the white wine and boil until almost evaporated.
Add 4 cups of chicken stock to the casserole and simmer until the vegetables are tender, about 30 minutes. Discard the herb sprigs. Add the heavy cream and bring to a simmer.
In a blender, puree the soup until smooth. If the soup is too thick, add the remaining 1/2 cup of stock and rewarm. Season with salt and white pepper and serve hot, with crusty bread.