Made these yesterday and they are a new favorite! Just wondering if the problems with the dough coming together could relate to the softness of the butter. After reading the article about Dorie Greenspan/sables and having acquired the Bouchon Bakery cookbook, I noted the use of the term pommade. Keller mentions using a torch to the bowl of the mixer to help soften the butter to the point that when creamed with the sugar it becomes almost like mayonnaise. I tried the technique with these and had great results.
1.Made sure butter was at room temperature and creamed with the sugar until fluffy (the butter actually went from yellow to light yellow);
2.Made sure the egg was also at room temperature;
3.Finely chopped the chocolate and processed it with the sifted flour/cocoa/baking soda mixture in the food processor (no lost fingers from grating, no sticking, no clumping and the entire mixture turned into a nice powder);
4.The batter held together after mixing but I did put it in the fridge while I was lining my pans and looking for my rolling pin;
5.I rolled the batter in halves; I took the first half of the dough from the fridge and rolled it in between two sheets of parchment paper (no sticky mess, no extra flour);
6.I dipped my cutter in cocoa powder (to prevent sticking);
7.I saved the scraps from the 1st & 2nd rollings for a 3rd (even 4th) rolling and was concerned the scraps would become overworked and turn the later generation sables into rock hard discs. But au contraire! The last batches were just as delicate and layered as the first two!