In a mixing bowl, combine the butter, peanut butter and icing sugar. Add the chopped pistachio and puffed rice. Mix well. Refrigerate for at least 1 hour. Shape mixture into 2.5cm-diameter balls should it crumble, refrigerate the mixture again before reshaping.
Freeze the rice balls for 15 to 20 minutes before dipping in the melted chocolate and rolling in the chopped pistachios. Place in paper cups and refrigerate until ready to serve.
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