1Mix the sugar, cinnamon, pumpkin pie spice, and salt together.
2Sprinkle about half of the cinnamon sugar evenly over your work surface.
3Place the puff pastry on top and sprinkle the remaining cinnamon sugar over the pastry. Gently roll it out just enough to press the sugar into both sides.
4Starting with one long side, fold the pastry about 1/4 of the way toward the center. Fold it over again so it reaches the center. Repeat with the opposite side so both folded edges meet in the middle. Fold one half over the other like a book.
5Chill for 20–30 minutes, until firm.
6Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
7Cut the chilled pastry into 1/2-inch slices and arrange them cut-side up on the baking sheet, leaving plenty of space between each one.
8Bake for 10–12 minutes, then carefully flip each palmier.
9Bake for another 5–7 minutes, until deeply golden, crisp, and caramelized.
10Transfer to a wire rack and let cool. They will become crispier as they cool.