Black Truffle Butter
Shave half the truffle into thin slices and cut into a very fine dice. Incorporate truffles with the softened butter.
Season to taste with salt, white pepper and lemon juice. Roll into cylindrical shape in parchment paper or saran wrap.
Refrigerate until ready to use.
Preheat oven to 350ºF.
In a small saucepan, heat olive oil over medium heat. Add the mushrooms and garlic; sauté for about one minute. Season with salt and pepper.
Transfer the mixture to a large casserole dish and add the chicken stock. Over low heat bring the liquid to a boil. Cover and simmer for 2 to 3 minutes. Remove from heat and set aside.
Season each side of the Ling Cod with salt and pepper. Heat the olive oil in a frying pan over high heat. Add the cod portions and sear until golden.
Remove cod from heat and place inside the casserole dish on top of the mushrooms. Cover casserole and place in oven for 3 to 4 minutes. Remove from oven; remove lid.
Add two tablespoons of the truffle butter, or truffle oil, to taste and let it emulsify into the liquid over low heat. Add the asparagus and pearl onions to reheat. Season the broth with salt and pepper.