There are several brands of ready made roux in our area. Without fail, the flour has settled in the bottom of the glass jar and has the consistency of concrete. If you don't take care, you'll shatter the jar first before getting out the roux, then you have to guesstimate how much oil to put with the flour. I can make a roux in about 12 minutes or less using the old Paul Prudhomme method from his very first cookbook. And I have about a 90% success rate the first time.