I use a minimal variant of Jeff Dwoskin’s modifications to the Toll House cookie recipe — (a) melt the butter first, (b) use yolks instead of whole eggs (I use one whole egg and one yolk; all yolks makes a dough that’s too dry for me), (c) chill the dough and (d) start the oven at 375, then take it down to 350 as soon as you put the cookies in. I haven’t really tried to vary these factors systematically and see what works better; I mostly trust Jeff, who claims they are provably optimal, and consumer reports, which concur.
Anyway, I had to bake some cookies tonight for a lab meeting tomorrow, and I discovered that we only had one stick of butter. I’d spent enough time in transit for one day, so I figured I’d sub oil. And, unshockingly in retrospect, the dough turned out too dry. (Exegesis for non-initiates: Butter isn’t 100% fat; oil is, so you substitute a bit less oil for any given quantity of butter; some of the rest of what’s in butter is water.) (Note to Thompson-Schill lab members: “Too dry” doesn’t mean “inedibly dry” or even “dry to the point of less than deliciousness,” only “too dry to pick up all the chocolate chips.” Be of good cheer.) I only bother to post about this because, given the modifications I use, the fix is obvious: Just use two whole eggs. Bah.