Mixing: Please Read the Note Below Regarding Mixing in a Planetary Mixer. Place all the ingredients except the cold butter in the mixing bowl. Begin the mix on first speed until the ingredients are incorporated, then turn the mixer to second speed. Mix until the dough is strong and tough, 5 to 7 minutes in a spiral mixer.
Meanwhile, take the cold butter and beat it with a rolling pin until it is pliable. To test for pliability, press your index finger into the butter before pounding with the pin, and notice how firm and cold it is—you can barely make an indentation. Now, pound the butter flat with the rolling pin (preferably not a ball-bearing pin) along its entire length and press your finger into the surface again. In just a few seconds, the butter will have gone from completely hard to pliable but still quite cold.
When all the butter is ready, and the dough is strong, add the butter, bit by bit, with the machine still on second speed. There is no need to wait for one addition of butter to be incorporated before adding the next portion. Once all the butter is in, the dough will be a bit confused, a little uncertain how to react to all that butter, and it will break. Soon enough, it will sort things out and begin to become smooth and satiny. The amount of time it mixes once the butter is incorporated will vary, depending on the mixer. Generally, you can expect the dough to mix for 8 or 10 minutes once the butter is added. Mix until the dough “sheets” fully. To test for sheeting, take a piece of dough about the size of an apricot. Holding it in both hands, gently and gradually begin to stretch the dough out. When it is sheeting fully, you will be able to coax it out into a thin, almost transparent, sheet. This means the dough is mixed. (And if you find yourself covered with goose bumps, you are not alone. I always marvel at the dough at this point—with all that butter, how can it do that? It seems to be ignoring some fundamental law of physics.) Transfer the dough into a lightly floured dough bucket or container, tuck plastic around the dough so that no air can enter, and let stand at room temperature for 1 hour. Fold the velvety dough, place it back in the dough bucket or container, cover again with plastic, and refrigerate. Degas 2 or 3 times over the next several hours. It is best to make the dough 1 day ahead and chill it thoroughly before using it. Unless you are baking in a food competition and facing time constraints, let the dough chill overnight and use it the next day.
NOTE: Mixing in a Planetary Mixer. It is much more difficult to adequately develop the dough when mixing in a planetary- (or stand-) style mixer. Here is a technique that can help: When beginning the mix, rather than adding all the ingredients except the butter, hold back half or more of the sugar as well. This will keep the developing dough in a firmer condition (although it seems counter-intuitive that holding back a dry ingredient makes the dough firmer and not looser, in fact sugar functions as a liquefying ingredient in doughs, and when all the sugar is added at the outset, the result is a looser-textured dough that will be more difficult to develop). Once a strong gluten network has developed, add the remaining sugar, mix until it dissolves into the dough (2 minutes should suffice), and then proceed to add the pliable butter.