Coarsely chop 12 ounces of chocolate; set aside. In a saucepan, heat cream over low heat until bubbles form around sides of the pan. Remove from the heat; add chopped chocolate, stirring until melted and smooth.
Cool to room temperature. Stir in butter and extract. Cover tightly and refrigerate for at least 6 hours or until firm.
Grate remaining chocolate; place in a shallow dish. Add nuts; set aside. Shape tablespoonfuls of chilled chocolate mixture into balls. Place on waxed paper-lined baking sheets. (If truffles are soft, refrigerate until easy to handle.) Roll truffles in chocolate-nut mixture. Store in an airtight container in the refrigerator.
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