Preheat the oven to 350°. Heat the olive oil in a roasting pan set over 2 burners. Add the fennel bulbs and cook over moderately low heat, stirring occasionally, until the fennel softens slightly and is just beginning to brown, about 20 minutes. Scatter the garlic, olives, cardamom and thyme over the fennel and season generously with salt and pepper. Pour the chicken stock into the roasting pan and bring to a boil over moderately high heat. Turn off the heat.