Shape the butter into 6.5" square flat block and place into the freezer until a few minutes before the lock-in.

Start by mixing the leaven and poolish into the milk, then mix everything but the butter. Allow to rest for 5 to 10 minutes, then cut in the butter and mix until smooth.

Move the dough to the refrigerator to chill until the lock-in

Ensuring the butter and dough are a similar consistency, lock in the butter. Turn the dough 90˚ clockwise Roll the dough out to a 19" x 6.8" rectangle.

Rotating the dough 90˚ clockwise from the last fold, so that the spine of the fold is to the right and the last-folded flap is on top, again roll out to a 19" x 6.8" rectangle. Fold the top and bottom halves to meet in the middle, then fold in half again.