When the dough and the butter block are both chilled but still flexible (60F to 70F / 16C to 21C), it’s time to lock the butter into the dough: On a lightly floured surface, roll the dough out to a rectangle 12 by 10 inches and ⅔ inch thick. If necessary, turn the rectangle so that one of the shorter ends is facing you.
Peel the paper back from the top of the butter block, leaving it on the paper so that you can use it to help you to guide it onto the dough: Invert it onto the bottom half of the dough, positioning it so that there is a 1/2 to ¾ inch margin of dough around the sides and bottom of the butter block. Fold the top of the dough down over the butter block so that it meets the opposite edge of the dough. Press the edges of the dough together firmly all the way around to seal, then fold the excess dough at the bottom and edges under itself. You should now have a firm but pliable rectangular package of dough (about 6 by 10 inches) enveloping the butter block. If the dough and/or butter block are too soft to proceed with rolling and folding, cover the dough with plastic wrap, place it on a parchment-lined baking sheet, and chill it for about 30 minutes.
Line a baking sheet with parchment paper. On a lightly floured surface, roll the dough out to a rectangle 13 by 19 inches and 1/2 inch thick. If you’re having a hard time rolling the dough, it’s probably too cold. Let stand at room temperature for 10 to 15 minutes. On the other hand, if bits of butter are breaking through the surface and getting all melty and squishy, it’s too warm; return it to the refrigerator to firm up.
There are two kinds of folds used for making puff pastry: the 4-fold and the 3-fold. You will be making a 4-fold, a 3-fold, a 4-fold, and final 3-fold. (If this sounds confusing, it will all make sense soon!) To make the first 4-fold, position the dough so that one of the long sides is facing you. Fold the left edge about three quarters of the way over the dough. Fold the right edge one quarter of the way over the dough so it meets the left edge. The dough will now look somewhat like an open book with an off-center spine. Fold the larger side over the shorter side. You will now have 4 layers of dough. Transfer the dough to the parchment-lined baking sheet. Brush all loose flour off the surface of the dough. Cover the baking sheet with plastic wrap and refrigerate the dough for about 30 minutes—you want the dough to relax and return to the ideal temperature.
Now make the first 3-fold: On a lightly floured surface, roll the chilled dough out again to a rectangle 13 by 19 inches and 1/2 inch thick. With one of the long sides facing you, fold the left edge one third of the way over the dough. Then do the same with the right edge, folding it one third of the way over so that it rests on top of the piece you just folded. You will now have 3 layers of dough. Brush away the excess flour. Return the dough to the baking sheet, cover, and refrigerate for another 30 minutes.
Make another 4-fold. Return the dough to the baking sheet, cover, and refrigerate for about 30 minutes.
You’re almost done! Make another 3-fold. Return the dough to the baking sheet, cover, and refrigerate for about 30 minutes.
Once the dough has chilled, divide it into two even pieces. The dough can be used immediately, or wrapped tightly in plastic wrap. It can be refrigerated for up to 3 days or frozen for up to 3 months. Thaw in the refrigerator overnight before using.