Not to hijack a thread (pun intended and not) but have you ever tried making roux in cast iron in an oven? I use that method for all of mine now. I haven't burned a single speck of roux since I started doing that. 350* and stir every 15-20 minutes. I know you make prodigious quantities of the stuff at one time, but for a single batch needed, oven method cannot be beat.
Yes I have made a roux in the oven...and it does work awesome. For a small batch, it is easy, but when doing large batches like I do, The pot is cumbersome to move when you have to stir when doing it in the oven.