How to Make It
In a medium saucepan of boiling salted water, cook the potatoes until just tender, about 15 minutes. Using a slotted spoon, transfer the potatoes to a plate and let cool slightly. Separate the brussels sprouts into leaves. Add the leaves to the boiling water and cook until they turn bright green, about 2 minutes; drain. Peel the potatoes and cut them into 1/2-inch dice.
In a large skillet, cook the bacon over moderate heat, turning once, until crisp, about 5 minutes. Drain the bacon and coarsely chop it. Pour off all but 2 tablespoons of the bacon fat from the skillet. Add the potatoes and cook over moderate heat until browned on the bottom, about 4 minutes. Stir the potatoes and cook until browned all over, about 3 minutes.
Add the onion to the skillet and cook over moderate heat, stirring, until softened and starting to brown, about 4 minutes. Add the brussels sprout leaves and the bacon and cook, stirring, until heated through, about 1 minute. Season with salt and pepper.
Meanwhile, in a medium saucepan, boil the apple cider with the applejack and butter until the cider glaze is reduced to 2/3 cup, about 25 minutes.
Preheat the broiler. Season the salmon steaks with salt and pepper and brush them on both sides with the cider glaze. Arrange the steaks in a broiler pan or on a rack set in a rimmed baking sheet. Broil the salmon for about 8 minutes, brushing occasionally with the glaze, or until crisp and just cooked through.
Reheat the brussels sprout hash. Brush the salmon steaks with any remaining cider glaze, then transfer to plates and serve with the hash.