While purée is chilling, line another baking sheet or tray with parchment paper. Melt chocolate (see
Tips), then remove from heat. Transfer chocolate to a small sealable bag and seal, pressing out excess air. Snip off tip of one corner to form a tiny hole. Pipe 1/3- to 1/2-inch-long ovals of chocolate onto sheet, flattening them slightly, to resemble watermelon seeds. Freeze chocolate “seeds” on sheet until very firm, about 30 minutes. Working quickly, loosen “seeds” from parchment with an offset spatula or knife and transfer to a small bowl, then freeze, covered.