Place the dough onto a lightly-floured surface and position the butter block in the middle so it has thin dough borders on the left and right sides.
Fold the bottom and top dough overhangs towards the center of the butter block so they meet. Pinch them and the dough on the sides to seal the butter inside.
Rotate the slab 90 degrees left and add some flour underneath. Gently beat it with the rolling pin, elongating the dough and filling the possible space inside the slab with butter. Roll it to make it even and adjust the ends so the dough keeps a rectangular shape. The slab should be approximately 7” by 14” or 17cm by 35cm.
Brush off the visible white flour (do this every time before folding the dough).
Perform a four-fold turn, aka a book fold: fold the bottom and top ends towards the center of the dough, leaving a small gap in between them. Then, fold the slab in half. It should look like a closed book. Wrap it in plastic wrap and refrigerate for 1 hour.
Remove from the fridge and place the dough on the rolling surface, rotating it 90 degrees left so the book opening is on the left side. Roll the dough into a 7” by 14” or 17cm by 35cm slab. If any air bubbles appear on the surface, gently burst them with a toothpick and seal the dough again to prevent the butter from leaking out down the road.
Do a three-fold turn, aka letter fold or simple fold: fold the bottom third over the middle third. Then, fold the top third over the bottom third that you folded previously. From the side, this fold should look like a spiral. Wrap it with plastic wrap and refrigerate for 1 hour.
Turn the dough 90 degrees to the left, so that the exposed end of the spiral is facing the left side, before you start rolling. Repeat the three-fold turn and refrigerate for 1 hour. Alternatively, you can wrap it tightly in plastic wrap, freeze it for 40 minutes to slow down the yeast, and then refrigerate it for 6-8 hours (overnight) to bake first thing in the morning. In total, you should perform one four-fold and two three-fold turns.
Now, your dough is ready to be rolled out, cut, shaped, proofed for 20 -30 minutes or until puffy, and baked. The baking instructions will vary depending on the size and type of pastry you want to make, but in general, this dough is baked at 375F (190C).