Position an oven rack in the lower third of the oven and heat to 325 degrees F (163 C).
Using a medium bowl - start with the butter, beat until creamy. Combine sugar, cocoa powder and the salt.
Once mixed, gradually start adding the eggs, beating one by one until they are fully blended in the mix.
Add in your vanilla, and gradually sift in the flour and baking powder. Once all in incorporated begin to dad the walnuts or pecans. You may want to beat them first until they become very small before putting them into the mixture.
Add everything to the mixture, I decided to add chocolate chips (both milk and white) for a more moist texture.
Once all is mixed together, grease down the pan you want to use and bake 20 to 25 minutes or until a toothpick can be inserted into the center and come out almost clean (you want it to be a little moist with batter).
Once cooked, put on a rack and allow to cool.
For the topping, in two separate bowls, put both white and dark chocolate and allow to melt. Once melted, place on the cool fudge and begin to decorate.