It is a very hydrated dough mixed with ice water, then put straight into the refrigerator. You bring the dough out the next day to proof. The theory, as Reinhart explains, is that the cold stops the yeast from getting started until after enzymes get a head start in breaking down starch into sugar. As a result, there is more sugar for the yeast to work with, and some of the sugar stays in the dough for flavor, texture and for the crust.
It worked really well for me the first time, which is a good sign. My baguettes were nicely brown and crusty (just using a pizza stone). This will be great in a brick oven.
Here is the basic recipe:
500 gram flour
400 grams ice water
2 tsp salt
2 tsp yeast
That's right. 80% hydrated.
When the dough has doubled the next day (it takes a long time to warm up and proof), pour/scrape the ball into a floured surface, gently pull to a 6"x8" oblong, then cut into three strips that become the baguettes. Let them rest a short period (5-10 minutes), slash and bake.