Step 1Make the court bouillon: Combine the apple cider, cider vinegar, cinnamon stick, horseradish, clove, vanilla and onion in a 12-inch skillet. Bring to a low simmer and cook 10 minutes.
Step 2Season the fish with salt and pepper, add it to the court bouillon, cover the pan, and gently cook 3 minutes.
Step 3Remove the fish and keep it warm. Strain the court bouillon into a small saucepan and reduce it by half over high heat, 5 minutes. Whisk in the butter and season with salt and pepper. Add the diced apple and radishes and cook 1 minute.
Step 4Place the fish in the center of a deep dish or pasta bowl. Spoon the garnish and sauce over the fish and sprinkle with the chopped chives.