3) In a small bowl combine crabmeat, Brie cheese, 1 tbsp fresh chopped herbs, 1 tbsp shallot, 1 tsp minced garlic and salt and pepper, to taste. Season both sides of halibut with salt, pepper and some of the fresh herbs.
4) Lay on an individual piece of plastic wrap, twice as big as the fish piece, flesh side down. Lay salmon piece on top of halibut, directly in the middle. Season with salt and pepper. Spread 1/4th of the crab and Brie mixture in the middle of the salmon. Do this with all 4 pieces of fish. Take plastic wrap that the fish is laying on and wrap fish into a tight roll, twisting the ends to make a tube . Refrigerate.
5) Toss yams, roughly chopped garlic, thyme sprigs and olive oil in a bowl until completely coated. Season with salt and pepper. Spread evenly on a sheet pan and roast in a 180C/Gas 4 oven for 15 to 20 minutes or until tender.
6) While yams are roasting combine Riesling and 2 tbsps shallots in a small saucepan. Reduce by 3/4 over medium-low heat. Whisk in butter a little at a time until completely combined. Once all the butter is beaten in, remove from heat and season with salt.
7) When yams have about 10 minutes left to finish, take fish rolls from the refrigerator and slice each roll into 3 or 5 equal sections. Remove plastic wrap after cutting and lay shingled out on well greased sheet pan and put into oven with yams.
8) When yams are done, fish should be done as well. While fish and yams are cooking, heat saute pan with 1 tbsp whole butter. Once hot, drop mushrooms into pan and saute over medium-high heat until crispy and tender. Season with 1 tbsp shallot, 1/2 tsp minced garlic, salt and pepper, to taste.
9) Remove yams and fish from oven. Place a 7 or 9-cm ring mold in center of plate and fill with roasted yam hash, pressing down firmly. Remove ring mold. Place mushroom mixture on top of yam cake, allowing it to spill slightly over the side. Take fish roll and shingle in front and up yam cake, creating some height with the back piece of fish. Drizzle Riesling butter over front edges of fish slices. Garnish with 2 chive sprigs and serve.