1 medium fennel bulbtrimmed, halved, cored and thinly sliced
1 medium onion, thinly sliced
4 scallions, white and tender green, thinly sliced
1 garlic clove, thinly sliced
1/2 cup chicken stock or canned low-sodium broth
Salt and freshly ground pepper
5 tablespoons cold unsalted butter, cut into pieces
In a large pot of boiling water, blanch the lobsters until they start to turn pink, about 1 minute. Drain and let cool. In a small bowl, cover the saffron with the white wine and let steep for at least 30 minutes.
Heat 2 tablespoons of the olive oil in a large nonreactive skillet. Add the fennel, onion, scallions and garlic and cook over moderately low heat, stirring, until tender, about 20 minutes. Add the saffron mixture and boil over moderately high heat until the wine evaporates. Add the stock and boil until reduced by a third. Season with salt and pepper.
Meanwhile, preheat the oven to 450°. Halve each lobster lengthwise. Remove the brain sac, sand sac, tomalley and roe, if necessary. Crack the claws well all over.
In a large, heavy-bottomed roasting pan set over 2 burners, heat the remaining 3 tablespoons oil until almost smoking. Add the lobsters, cut side down, and cook over moderately high heat until the meat is browned, about 3 minutes. Transfer to the oven and roast for about 5 minutes, or until the meat is cooked through. Transfer the lobsters to a platter, season with salt and pepper and keep warm.
Rewarm the fennel mixture. Remove from the heat and stir in the butter, a little at a time, until the sauce is thickened. Season with salt and pepper. Divide the fennel mixture among 4 large plates and arrange 2 lobster halves on each.