Preheat the oven to 400 degrees F. In a saute pan, over medium heat, add 2 tablespoons of the olive oil. When the oil is hot, add the onions. Season with salt and pepper. Saute for 1 minute, or until slightly wilted. Add the mushrooms. Season with salt and pepper. Saute for 2 to 3 minutes. Add the garlic, prosciutto and parsley. Continue to saute for 1 minute. Remove from the heat and drizzle the relish with the truffle oil. Set aside. Season the fillets with Essence. Rub 1 teaspoon of the mustard over each fillet, covering completely. Drain the potatoes. Season with salt and pepper. Divide the potatoes into 4 equal piles. Wrap each fillet with one pile of the potatoes, tightly. Cover the potatoes with a damp cloth until ready to use. Repeat the process until all of the potatoes are crusted. In a large oven-proof saute pan, heat the remaining oil. When the oil is hot, carefully lay the fillets in the hot oil. Pan-fry for 3 to 4 minutes on the first side, or until the crust is golden. Flip the fillets over and place the pan in the oven. Cook for 4 to 6 minutes. Remove from the oven. To serve, spoon the sauce in the center of each plate. Place the crusted fillets in the center of the sauce. Spoon the relish over the fillets. Serve immediately.
Heat a large nonreactive skillet over high heat. When the skillet is hot, add the wine, lemons, garlic, and shallots. Cook for 3 minutes, breaking up and mashing the lemons with a wire whisk. Stir in the salt, pepper, Worcestershire, and hot sauce and cook until the mixture is somewhat syrupy, for about 3 minutes. Stir in the cream and cook for 1 minute.
Over low heat, whisk in the butter a few pats at a time. When all of the butter has been added, remove from the heat, but continue whisking until all of the butter is incorporated into the sauce.
Strain the sauce, pressing all of the liquid into a bowl. Stir in the parsley. Serve immediately, or keep warm for a few minutes until ready to use.
Combine all ingredients thoroughly and store in an airtight jar or container.
Recipe from "New New Orleans Cooking", by Emeril Lagasse and Jessie Tirsch. Published by William and Morrow, 1993.