Pop the popcorn according to package instructions. While hot, carefully open package and dump into a large bowl.
Toast the pumpkin seeds in a large skillet over medium-high heat, until browned and popping, tossing and stirring occasionally, about 4 minutes. (Do this in batches, if needed.) Add to the popcorn.
Make caramel: Warm the cream over low heat and keep warm while you cook the sugar. Put the sugar and corn syrup and in a deep, heavy-bottomed large saucepan. Cook over medium heat, stirring occasionally until the sugar dissolves. Stop stirring, raise heat to medium-high, and simmer until the sugar reaches the hard crack stage, or 305 degrees F on a candy thermometer, about 7 minutes.
Whisk the butter and salt into the sugar mixture. Gradually pour in the cream and vanilla taking care since the mixture will bubble up. Reduce the heat to medium and continue to cook, stirring occasionally, until the sugar reaches soft ball stage, 240 degrees F on the thermometer, about 5 minutes more. Immediately remove from the heat and stir in the cinnamon and cayenne. Cool for about a minute. Pour caramel over the popcorn and stir to evenly coat.
When the popcorn is cool enough to handle, coat your hands with some butter and shape into 4-inch balls. Wrap in waxed paper and tie with a string, if desired. Serve or store covered at room temperature for up to a week.
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