1. Preheat oven to 300ºF. Line 2 baking sheets with foil. Melt butter. Mix cinnamon and sugar together in a small bowl.
2. Pour melted butter over popcorn in a large bowl; toss to coat. Immediately sprinkle with sugar mixture; toss to coat. Divide popcorn between sheets; spread in a single layer. Bake for 30 minutes, shaking pans every 10 minutes. Cool.
3. Place cream and chocolate chips in a heatproof bowl set over a pan of simmering water. Cook, stirring occasionally, until melted and smooth, 8 to 10 minutes. With a fork, drizzle chocolate mixture over popcorn and let stand until set, about 30 minutes. Break up any clumps and store at room temperature in an airtight container for up to 5 days.
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