Line a baking sheet with parchment. Put the chocolate in a small microwave-safe bowl, and microwave in 30-second increments, stirring after each, until smooth. Transfer the melted chocolate to a mug.
Put the walnuts in another small bowl. Peel the bananas, trim the ends and cut each into six 2-inch pieces. Dip each piece halfway into the chocolate, and let any excess drip off. Roll the chocolate-dipped ends in walnuts, then set them on the prepared baking sheet. Refrigerate to set the chocolate. (The bananas can be refrigerated up to 2 hours.)
Whip the cream in a small bowl until soft peaks form. Add the preserves, and stir to incorporate. Transfer the mixture to a pastry bag fitted with a large star tip. Pipe a star-shaped dollop on top of each banana. Garnish with a piece of cherry and sprinkles.
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