If using store-bought puff pastry, you will have 2 sheets ready to use. If using homemade puff pastry, divide the dough into 2 equal pieces before starting.
Lightly flour your surface. Roll out one puff pastry sheet into a rectangle of about 28x30 cm (11x12 in). Sprinkle generously with around 1/2 of the sugar and roll lightly with a rolling pin to press the sugar into the pastry.
Fold each long edge inward by about 1/6 of the width. Sprinkle with more sugar and press it in gently.
Fold each long edge inward again, this time by about 1/4 of the width, so the edges meet neatly in the center. Sprinkle with more sugar and roll lightly to press it in.
Fold the pastry lengthwise in half, like closing a book. Very gently press along the length of the roll to compact it slightly but don’t flatten.
Using a sharp knife, cut the log into slices about 6 mm (1/4 in) thick. Place slices cut-side up on a parchment-lined, light-colored baking sheet. Repeat the process with the second sheet of puff pastry.
Place the tray of palmiers in the fridge for 15–20 minutes while the oven preheats to 200°C (400°F).
Bake for around 20 minutes, flipping halfway through so both sides caramelise evenly. They’re ready when puffed, deep golden, and caramelised.
Let cool on the tray for 5 minutes, then transfer to a rack. Store in an airtight container for up to 3 days.