I am an amateur cook. While I have been making a couple different sauce recipes, I have been using flour to thicken it. To deal with lumping, I have been try several methods. One successful one has been to mix the flour into the cold broth. I simply add the flour to the broth and whisk out any dry lumps. This method works because the gluten globules don't form without heat.
However, I don't see this method referenced in any method. Instead I have been told to only mix the flour in oil or knead it into butter.
Is there a reason why the flour + broth method isn't recommendable?
Does the method to make a roux not work if there is liquid in the mix?