Pre-made instant roux mix (powdered roux) is becoming popular as a way to quickly prepare a gumbo or stew. I've done some experimenting with powdered roux to be able to explain to you the easiest methods to use it. These methods use Tony Chachere's Instant Roux Mix, I haven't tried any others yet. Tony's Roux mix has some seasonings in it already so be careful with additional seasonings. Method 2 is the easiest!

Method 1

Let's say you'll be cooking a one gallon gumbo. We normally say "first you make a roux". This is not necessarily the case with powdered roux. You can add it last if you wish as you can with roux in a jar. 

Chop your vegetables as usual. Sauté them in oil until wilted. Brown the meat on the side or on the veggies. Cook until almost done.

Now the roux.

Use about 1/2 cup of powdered roux. Put the powdered roux in a 2 cup measure. Add a tablespoon (doesn't have to be exact) of water and stir. 

Add the same amount of more water and stir. You want to make a well mixed paste. I just run the tap water real low and work the cup in and out adding a tiny bit of water at a time. CAUTION: If you go too fast or add too much water at a time you'll be fighting lumps.

Continue the add - stir routine until you get about 1 - ½ cups of liquid roux. You can add increasing amounts of water as you go. 

This method is no different from any other powdered mixes. The idea is to start with a paste and bringing the mix to an increasingly liquid form. If you don't prepare the roux in this manner you'll wind up with lumps.

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Add about 6 cups of water or stock to your gumbo and bring to a boil. 

This is a Chicken-Andouille Gumbo that I've done "in reverse". Notice the light color (no roux in it).

Slowly pour 2/3rds of the roux into the pot and stir well. Bring it to a boil. This is extremely important. Bringing the roux to a boil will thicken it. The boiling holds true for a homemade roux also. 

Add more water or stock and stir well. Here is the Gumbo with roux added. See the color change? 

Continue to boil and stir for about 3 minutes. Add water to the amount you want. If it's not thick enough add the remainder of the roux. Some people like thick gumbo some like thin. Do it like you want.

Remember how much more roux you mixed so you'll know how much to use for your next gumbo.

If you're going to use powdered roux mixes you'll have to do some experimenting on the amounts of roux mix to make the size and thickness stew or gumbo you normally make. In general, use the same amount of instant roux mix as you would flour in a traditional roux.

Method 2 (the easiest)

Bring the liquid (gumbo) to a boil and stir the pot making the liquid swirl. While the liquid is moving take the powdered roux in the other hand and sprinkle the roux in very lightly. Don't stop stirring while you sprinkle! Boil the liquid again for a few minutes and see how thick it is. Add more using the same method if needed.

Note:  CAUTION: If you sprinkle too much at one time it will lump up. 

Enjoy...