To make chocolate peanut cluster candy in a slow cooker, combine all the ingredients except vanilla in a 5-quart slow cooker.
Cover and cook on LOW for 2 hours or until the chocolate is melted. Stir the chocolate and nuts, and add vanilla, stirring well to coat.
Drop the candy by heaping teaspoonfuls onto wax paper. Making candy in a slow cooker works great is ideal because you can keep the chocolate mixture warm while you're spooning it out onto the wax paper.
Let it the candies stand at least 2 hours or until firm. Store in an airtight container.