A roux is a term used for a mixture of flour and liquid that is used to thicken sauces and/or in baking. In soul food there are three kinds of roux:
Which you use depends on what you want to make, but because grains should generally be fermented, milk roux and water roux are the preferred ones for nourishing soul food. You would use a butter roux only in recipes that will be slow cooked, such as certain gumbos or slow cooked stews that you want to have a creamy texture. Something that will cook for less than 2 hours should have a water or milk roux.
A butter or fat roux should be made with equal parts butter or ghee and plain white flour by weight. Soften the fat, and press the flour in with your fingers. If you won't be using it immediately, wrap it up tightly and keep it in the refrigerator. It will keep for about a week like this. In some places, you can buy ready made butter roux that will keep longer.
A water roux is one part white flour, corn or potato starch, or oat flour to three to five parts water. Mix the flour with very hot water, and let it ferment for at least 7 hours before using. It will keep in the refrigerator for about a week.
Water roux can be used to thicken sauces, but it is also useful in baking. You can use it instead of the water or milk you would usually add in a conventional recipe. It will make what you bake with it lighter because the starch has had time to ferment and "blossom". It also has good bacteria and organic acids that will give it a boost of fluffiness.
A milk roux is one part white, oat, wheat, barley, amaranth, or teff flour to three parts whole milk, yogurt, or sour cream. Just whisk it together, and leave it to ferment overnight in the refrigerator. This can also be used in sauces or in baking.
In some of the recipes on this site, one of these types of roux may be called for.