Cook the lobsters under the broiler, approximately 1 minute per ounce. Ours took almost exactly 5 minutes — you’ll know they’re done when the lobster meat has turned white and is no longer translucent. While your crustaceans are cooking, it’s a good time to preheat a cast-iron skillet for the steak. Cast iron can withstand the heat, so it’s fine to place it in the oven while the broiler is going.