Just as cornstarch is used for thickening pie certain pie fillings, flour high in starch is said to work best at thickening 'sauces' (non cream) and braises. That's where cake/pastry flour comes in. As a result of having a higher starch and lower gluten content, these high starch flours both seem to thicken the liquid quite well without giving a gummy mouthfeel that flours higher in gluten (and lower in starch) seem to provide. Also I used, for the first time, stale rye bread to thicken some plain ol' braised chicken thighs and it seemed to work quite well even though Mr. Keller might not have approved!!!!! I got the idea from the book entitled The Medieval Kitchen by Redon, Sabban and Serventi. And also in a thread that follows, My First Fried Chicken, checkout this comment made by BDL: It helps to use a fairly soft flour for the coating. If you're using AP flour, cut it in half with cake flour; or cut it with some corn starch. About four parts flour to one part corn starch. You'll find that you get a better texture if you use a little baking soda in the flour as well.