I know all that. I thought I already responded to this but it’s not showing up.
I’m just leading you on because I’m enjoying sparring with you.
And it’s spelled “roux” and not roue. You mix fat with flour (or other thickener) to help prevent lumpy gravy.
En Français, mademoiselle.
LOL...I wondered just where, exactly, down the garden path you were leading me, old friend.
And a roux is usually made from butter and flour. It adds a "nuttiness" to gravies and other types of sauces. OTOH...one can also use arrowroot, cornstarch, or just plain old flour; however, as you said, these CAN make a gravy lumpy, if not thoroughly mixed well into the liquid.
Madame; if you please, monsieur.