Preheat oven to 350. Melt butter and cocoa in a small pan over the stovetop. Beat flour, sugar, vanilla, and the cocoa mixture in a medium bowl. Spray a round 4" deep cake pan with nonstick spray or butter. Pour mixture into pan. Puree chocolate bar and grahamcrakers. Sprinkle the marshmellows and pureed grahamcraker, chocolate mixture on the brownies. Bake for about 25 minuites or untill the marshmellows are lightly toasted.
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