How to Make It
In a skillet, cook 1 cup of the oil and the garlic over low heat until the garlic is pale golden and softened, about 7 minutes. Using a slotted spoon, transfer the garlic to a bowl and mash with a fork. Let the oil cool slightly, then add the cream.
In a saucepan, cover the potatoes with water and cook until tender, about 30 minutes. Let cool slightly, then peel the potatoes and pass them through a ricer or sieve. Alternatively, whip the potatoes with an electric mixer. Add the mashed garlic and the garlic-oil cream. Stir in the trout and season with salt and pepper.
Preheat the oven to 350°. Spread the brandade in a shallow 1 1/2-quart baking dish. Make shallow depressions in the brandade and spoon the remaining 1/4 cup of oil into the depressions. Bake for about 15 minutes, or until heated through. Sprinkle with the chives and serve warm.