Andy M.
Certified Pretend Chef
Nicholas Mosher said:...Preventing lumps is all about whisking like a madman and slowly trickling the liquid in until you have a consistency that of gravy...
I've never had to "wisk like a mad man".
When you have made a roux, the flour granules are coated with fat. This prevents them from sticking together to form lumps.
I add liquid to a roux wisking steadily to mix in the liquid until the consistency is uniform throughout. Lumps are not a problem.