In a large skillet, heat 1 tablespoon of the olive oil. Add the fennel, cut side down, season with salt and pepper and cook over moderately high heat, turning once, until browned on 2 sides, 6 minutes. Add the remaining 1 tablespoon of olive oil and the shallot, garlic, thyme and saffron and cook, stirring, until the shallot is softened, 1 minute. Add the stock, cover and simmer over low heat, turning once, until the fennel is tender, 12 minutes. Season with salt and pepper; discard the thyme.