Preheat your oven to 400°F and set the rack in the center position, then line two baking sheets with parchment paper.

In a small bowl, stir together the granulated sugar, ground cinnamon, and salt until evenly combined.

Sprinkle a clean, smooth work surface with 2 to 3 tablespoons of the cinnamon-sugar mixture, unfold one sheet of thawed puff pastry over the sugar, and gently roll it into a 9-by-12-inch rectangle.

Sprinkle 1/4 cup of the cinnamon sugar evenly over the pastry and roll gently over the top with a rolling pin to press the sugar into the dough.

Starting at one of the shorter sides, roll the pastry inward toward the center, then roll the opposite short side inward until the two rolls meet in the middle, pressing the two sides together lightly to form a log.

Repeat the rolling, sugaring, and shaping process with the second puff pastry sheet and the remaining cinnamon sugar.

Place the two rolled logs on a plate or baking sheet and chill them in the refrigerator for 10 to 15 minutes to make slicing easier.

Use a sharp knife to slice the chilled logs into 1/2-inch-thick pieces, then arrange the slices cut-side up on the parchment-lined baking sheets, leaving about 2 inches between them.

Bake for 12 minutes, until the bottoms are golden and caramelized, then carefully flip each palmier over and bake for another 5 minutes, until both sides are golden brown and crisp.

Let the palmiers rest on the baking sheets for a few minutes before moving them to a wire rack to cool completely so they firm up as they cool.