(The basis for all stews and gumbos.) Tony Chachere's "Cajun Country Cookbook"

Heat oil in heavy pot or Dutch Oven. When oil is hot, gradually add flour, stirring constantly until well mixed. Lower flame and continue stirring until chocolate brown. When roux is chocolate brown, removed from pot and set aside. If roux remains in the pot it will continue to cook and get too dark.

Always use warm water to dissolve the roux.

While you're at it, make more than enough as it keeps well in or out of the refrigerator.

P.S. The darker the roux the more intense the taste. I prefer mine the color of peanut butter.