Guinness Glazed Cod
In a shallow baking dish, pour half of the stout glaze over the halibut fillets and turn to coat thoroughly. Cover and refrigerate overnight, turning a few times. Reserve the remaining stout glaze.
Preheat the broiler. Bring a saucepan of water to a boil. Add the carrots and boil until just tender, about 4 minutes; drain. Pour the reserved stout glaze into the saucepan and boil over high heat until thickened and reduced to 1/3 cup, about 2 minutes. Add the carrots and simmer until glazed, about 1 minute.
Remove the halibut from the marinade and arrange the fillets on a rimmed baking sheet. Brush the halibut with olive oil and season with pepper. Broil about 4 inches from the heat until richly browned and just cooked through, about 4 minutes. Transfer the halibut to plates and serve with the Guinness-glazed carrots.