Pan-fried Tilapia with Tilapia Brandade, Green Pepper Sauce, and Mussels in Celeriac Vinaigrette

Cut each fillet into a 4-oz. (100-g) rectangle. Refrigerate. Rub the trimmings with salt and refrigerate for 45 – 60 minutes.
To make the duxelles, sweat shallot in butter in a saucepan. Add mushrooms, cook 5 minutes and add white wine. Reduce over low heat until no liquid is left. Season with salt and ground black pepper. Refrigerate.
In a pan, melt a knob of butter and sweat onion. Deglaze with white wine and bring to a boil. Add mussels to boiling liquid and cover. Cook 4 – 5 minutes until mussels open. Remove mussels from shells and refrigerate. Strain pan juices and set aside.
In a pan, bring juices to a boil. Reduce to ¾ of volume and add white poultry stock. Bring to a boil again and reduce to ¾ of volume. Add cream and reduce to desired consistency. Add green peppercorns, season and refrigerate.
In a pan, cook turnip with minced ¼ onion and a drizzle of olive oil. Purée in food processor. Add 35% cream and heat slightly. Blend and season. Press through a sieve and refrigerate. In a pan, reduce shallot and white wine over medium heat until no liquid is left. Refrigerate.
In a pan, bring water, sugar and lemon juice to a boil. Meanwhile, using a mandolin, slice celery into crescents about 3-mm thick. When syrup comes to a boil, pour it over celery. Marinate at room temperature for 10 minutes. Drain and refrigerate celery.
In a pan, sweat ½ garlic clove and shallot in drizzling of olive oil. Add milk and bring to a simmering boil. Poach tilapia trimmings 2 minutes in simmering liquid. Drain poached tilapia and beat with 1⅓ oz. (40 mL) olive oil in a round-bottomed bowl. Season and refrigerate brandade.
In a skillet, melt a knob of butter and sweat minced ¼ onion and ½ garlic clove. Add mushrooms and season. Cook until all liquid has evaporated. Add veal demi-glace and cream. Reduce until almost no liquid is left. Adjust seasoning and refrigerate.
Cut potatoes with a 1-in. (2.5-cm) round cookie cutter. Pour white poultry stock into a skillet. Add potatoes and season. Bring to a boil. Cover and bake in a 375°F (190°C) oven. When potatoes are done, drain and set aside. Reduce pan juices until almost thickened to coating consistency and set aside.
In a small round-bottomed bowl, combine 20 mussels with mustard, green onions, celeriac, wine vinegar and a generous drizzling of olive oil. Season and set aside at room temperature.
Heat sauce, turnip purée, duxelles and brandade.
Season 4 tilapia fillets with celery salt. In a skillet, cook fillets in a generous bit of butter. Meanwhile, reheat potatoes in their pan juices.
Presentation:
Place fillet on a slice of prosciutto in the centre of the plate and garnish with a spoonful of duxelles and a spoonful of brandade. Draw a line of purée, add mussels, marinated celery and potatoes. Spoon green pepper sauce over fish and put vinaigrette on the mussels.