INGREDIENTS
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3 oz. unsweetened chocolate, finely chopped
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4 tbsp. unsalted margarine, plus more for greasing
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1 (1-lb.) box confectioners' sugar, sifted
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1/2 cup plain mashed potatoes
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2 tsp. non-dairy creamer
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1 tsp. vanilla extract
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⅛ tsp. kosher salt
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1/2 cup finely chopped walnuts
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Rock candy (optional)