To roast the hazelnuts you should place them on a sheet pan and put them in a 400F oven for 2 to 3 minutes, or until the outside skin starts to break away. Rub the hazelnuts together so that the outer dark skins flake off. You do not want to toast them, you just want the skin to loosen up. In a large skillet place the butter and heat it on medium high until it has melted. Add the mushrooms and saute them for 4 to 5 minutes, or until they are brown. Add the 1/4 cup of sherry and deglaze the pan. Add the chicken stock. Cook the ingredients on medium heat for 12 to 15 minutes, or until the liquid is reduced by 1/2. In a small saucepan place the 3/4 cup of sherry. Cook it on medium high heat for 4 to 6 minutes, or until it is reduced by 3/4. Add the reduced sherry, salt, and pepper to soup, and stir them in. In each of 4 individual serving bowls place 3 of the Chicken-Hazelnut Quenelles. Ladle the soup on top. Sprinkle on the hazelnuts.