Do not preheat the oven quite yet.Melt the butter in a 3 quart saucepan over medium low heat.
Add 1/2 cup of the chocolate chips and quickly remove from heat. With a heat-resistant rubber scraper, gently stir until the chocolate chips have melted from the heat of the butter.Stir in the sugar and set the pan over low heat, stirring gently for about 2 minutes or just until the mixture is shiny and sugar has started to dissolve. Do not let it boil.
Remove from heat and stir in the packet of Black Silk.
Let cool for about 20 minutes.While the chocolate mixture is cooling, preheat the oven to 325 degrees F.Grease an 8-inch glass dish and line it with parchment paper.
Mix together the cake flour (or White Lily), salt, baking powder and cocoa powder and set aside.After the chocolate mixture has cooled for about 20 minutes, stir in the eggs (still using the scraper), one by one. Do not beat them in, just stir gently. Stir in the vanilla.
Add the flour mixture and stir until it is incorporated, then stir in the remaining half cup of chocolate chips (making sure the batter is cool enough so that they don’t melt).
Pour the batter into the prepared pan and level it out.
Sprinkle with walnuts.
Bake on center rack for 35 minutes.
Let cool completely. I like to chill them for a while, but this is optional. Lift from the pan and cut into squares.
