Take 1 rectangle of pastry with the short side facing you and sprinkle lots of sugar on top of the pastry. Roll lightly with a rolling pin to press it into the dough. When you've pressed in as much sugar as the dough can hold, turn it over, add more sugar and lightly roll again. Repeat with the remaining pastry and sugar.
Roll each piece of pastry into a tight roll along the short end, without stretching, toward the center, then roll from the other end toward the center until the rolls meet in the middle. Repeat with the remaining sheets of sugared pastry.
Wrap in plastic wrap and refrigerate 20 minutes. Use a sharp knife to cut each roll into 1/2" slices.
Roll the slices very lightly and lay them out on the prepared baking sheets to the flat, swirly surface is facing upward. Dust with 10X sugar.
Bake 8-10 minutes, until pastry is crisp, caramelized, and golden brown. Keep a watchful eye on them to prevent burning.
Cool on a wire rack before serving.