Preheat oven 350 F

Melt chocolate squares and butter on low heat, take off from stove and let cool for 15 minutes. Add in beaten eggs, vanilla, salt, mix well. Add in mashed potatoes, mix well. Add in flour, mix well

Place/line a parchment paper on a rectangular pan, and pour batter into the pan Sprinkle with walnuts and white chocolates

Bake at 20-25 mins

Let cool to room tempt before slicing with knife or cookie/sandwich cutter

Enjoy