Skin fish, and cut into 7 ounces/210g portions. Rub with olive oil and season with salt on both sides; chill for 30 min. Clean, trim and cut zucchini in half. Slice into one millimeter scales; reserve. Overlap zucchini scales over each fish filet. Carefully, place each filet in separate freezer bag and slide it toward the bottom right corner of the bag. Immerse unsealed in cold water. As bag goes down, the air escapes compressing the fish in a gentle fashion; seal bag. If using a vacuum sealer, control the pressure accordingly. Chill prepared fish until ready to cook.
Cook fish using a sous-vide machine (Look up at Shop Page) at 135ºF/57ºC for 25 minutes for 1''/2.5cm thick fish. Cooking time may vary depending on the thickness of the fish. The fish can also be cooked in the steam oven at the same temperature for 20 minute. Leave fish in freezer bag until ready to serve. Reheat in water if necessary, and carefully remove from bag, drain fish on paper towel for a few seconds prior plating.
Cut off 3''/8cm of the asparagus, and peel. Save trimmings and peels to make an asparagus velouté. Bring to a boil water, salt, sugar and butter. Add asparagus and cook until fork tender, about 10 minutes.
Any mushrooms can be used for this recipe. Best are porcini and morels. Clean mushrooms accordingly and trim off foot. Save scraps for veggie stock. Meanwhile, clean and chop parsley and mince shallots. In a hot large skillet, sauté mushrooms with olive oil on high heat for 5 min. Add butter, and season with salt and pepper to taste. Add shallots and cook for an additional 3 minutes, then throw in parsley – transfer onto baking tray lined with silicone mat; keep warm.
Horseradish sabayon is nothing less than an Hollandaise sauce. First reduce wine and shallots to half a cup/125g; sieve. Place the bowl over a saucepan containing barely simmering water (Water should not touch the bottom of the bowl). Beat reduced wine with egg yolks until the mixture is thickened and doubled in volume (Do not over heat). Add horseradish, melted butter, and lemon juice whisking vigorously. Season with salt. Cover and place in a warm spot until ready to use.
Arrange on place some hot asparagus, and top with mushrooms. Add fish and horseradish sabayon. Bon appétit!