Drain the artichoke hearts and cut them into 1-inch wedges. In a roasting pan, toss the wedges with the chestnuts, garlic, lemon slices, broth, oil and thyme. Season with salt and pepper. Cover with foil and roast for 25 minutes, or until the artichokes are tender. Remove the foil and roast for 15 minutes, or until golden and the pan juices are evaporated.