Beurrage
butter block
The beurrage is the prepared sheet of butter enclosed in the détrempe before rolling. The butter is worked and shaped into an even rectangle, often between sheets of parchment, to a consistent thickness across its whole area.
What matters for lamination is not only the flavour of the butter but its plasticity when cold. Butter with a high fat content — 82% and above — stays pliable at lower temperatures and does not crumble under the rolling pin, which is why it is sold as dry or pastry butter. Butter with more water in it shatters under the same conditions.
The thickness and temperature of the block set up everything that follows. Too thin and it tears; too thick and it squeezes out at the edges. The target is dough and butter equally pliable: pressed with a finger, both dent without flowing.