Bring a large pot of salted water to a boil and place a bowl of ice water on the side. Add the fava beans and boil until tender, about 1 minute. Chill in the ice water, pat dry, and set aside. In a medium saucepan, combine the sachet, bay leaf, thyme, chicken stock, and lemon juice. To clean each artichoke, peel away the outer leaves and trim the stem to about 1½ inches in length. Using a sharp paring knife, remove the skin from the stem and any tough leaf remnants from the base. Immediately submerge in the liquid to keep from oxidizing. If needed, add water to keep artichokes submerged. With a mandoline, thinly slice half of 1 of the artichokes lengthwise into a small container, submerge with some of the liquid from the saucepan, and reserve for the garnish, chilled. Once all the artichokes are cleaned, bring to a simmer and cook for 20 minutes, or until tender. Remove from the heat and cool in the liquid. Use a spoon to scoop and discard the chokes from the artichokes and cut the flesh into ¼-inch dice. Transfer to a container and stir in enough cooking liquid to coat. Reduce the remaining liquid to 1 cup; adjust the seasoning with salt and pepper if needed, and reserve, chilled.