How to Make It
Line a rimmed baking sheet with parchment. Lightly oil a rubber spatula. Combine popcorn and nuts in a large bowl.
Melt butter in a heavy 2 1/2-quart saucepan over medium-high heat. Add maple syrup. Clip a candy thermometer to side of pan. Add 1/2 tsp. salt and bring to a boil. Reduce heat to medium to maintain a gentle boil and cook without stirring until thermometer registers 290ºF, 22 to 25 minutes. Watch syrup carefully toward the end to avoid scorching.
Remove syrup from heat. Stir in maple extract and cinnamon, then pour over popcorn mixture, stirring with spatula to help coat. Season with salt. Spread on lined baking sheet. Allow to cool completely before breaking into bite-size pieces. Store in an airtight container at room temperature for up to 3 days.