Melt the Chocolate in a double boiler. Place the walnuts on a parchment lined sheet pan and roast in the oven for 10 minutes at 350 degrees F.
In an electric mixer with the whisk attachment whip the cream cheese on high until light and fluffy. Lower the mixer to the lowest speed and slowly pour in the melted chocolate. Add the cocoa powder, powdered sugar and salt and whip until totally combined. Fold in the chopped walnuts. Pour the mixture into a lightly buttered or parchment lined 13"9 inch baking pan and chill overnight or until firm.
White Chocolate Ganache
Chop the white chocolate into small pieces and place in a heat safe bowl. In a saucepan bring the heavy cream, sugar, and butter to a boil. Pour the cream mixture over the chocolate and slowly whisk with a small balloon whisk until the chocolate is totally combined. Add the butter and whisk again until smooth and creamy. Pour the ganache over the fudge and let set up in the refrigerator for one hour.