Rinse the duck under cold running water both inside and out. Remove any excess fat at the cavity opening and at the neck. Use a sharp boning or butcher's knife to cut the back on either side of the spine. Remove the spine and reserve for stock. Cut through the breastbone of the duck to give you 2 halves. Cut the legs from each half as well as the first two digits of the wings. Set the legs aside, and cut the breasts in half horizontally.
Season the duck with 1 teaspoon of salt and the black pepper. Place a large Dutch oven over medium heat for 2 minutes, or until hot. Place the seasoned duck, skin side down in the pan and sear until golden brown, about 7 to 8 minutes. Turn the duck over and sear on the second side as well for an additional 7 to 8 minutes. Remove the duck from the pan and place on a platter while you make the roux.
Add the vegetable oil to the pan as well as the flour. Using a wooden spoon, stir the roux continuously over medium heat until the color of dark chocolate, about 20 to 25 minutes. Add the mushrooms, onions, celery and peppers and garlic to the roux and stir, gently until the mushrooms and vegetables are slightly wilted, about 4 to 5 minutes. Pour the beer over the vegetables and stir to incorporate. Add the stock/water to the pan with the thyme, bay leaves, Essence, cayenne pepper and the remaining 3 teaspoons of salt. Stir the pot well to ensure that the roux and the stock are well blended. Raise the heat to medium-high and bring the gumbo to a boil; then lower to a simmer. Return the seared duck pieces to the pan and cook (skimming any foam that may rise to the surface), for 1 hour and 30 minutes. After an hour and a half, remove the duck pieces from the gumbo and place on a platter to cool. Once the duck is cool enough to handle, remove the skin and meat from the bones and add the meat to the gumbo. Discard the skin and bones and re-season the gumbo, if necessary.
To serve the gumbo, ladle 1 cup into a heated soup bowl with 1/4 cup white rice. Garnish with the green onions and chopped parsley.
Combine all ingredients thoroughly.
Recipe from "New New Orleans Cooking", by Emeril Lagasse and Jessie Tirsch, published by William Morrow, 1993.