Shows how little i know!
I thought a roux was a roux was a roux!
I didnt know there was a different/ trickier one for gumbo!
Well a roux is a roux is a roux, but the colour of the roux is important in different types of cooking.
In gumbo a darker roux is generally accepted as the way to go, some people call this a black roux, but really it sort of looks a chocolate colour or dark brick red.
You can either do a dark roux safely, or quickly
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I choose safely and it takes about an hour to get a roux dark enough to use for gumbo, using either oil or clarified butter and patiently stirring (if you let it sit, it burns, if there's anything on the whisk or pan it burns etc.)
If you want to do it quickly you can heat oil to boiling, dump the flour in and whisk like hell and possibly explode it on yourself - NOT recommended!
You tend to use white rouxs in french cooking or just generally, for instance when I make gravy I make a light (blonde or peanut butter) roux and then whisk in stock (with juices from the roasted bird) and thus I make a velouté sauce
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Which is basically a light stock based gravy.
So yeah, if this is really good dark roux, it might be worth buying!