Heat a heavy pot over medium to medium-low heat
Add equal parts fat and flour, usually 1/2 cup oil or butter and 1/2 cup flour
Whisk or stir constantly until smooth
Keep stirring continuously to prevent burning
Cook until the roux reaches the desired color, from light blond to dark brown
For gumbo, cook the roux to a deep brown or chocolate color
Lower the heat if it starts to darken too quickly
Remove from heat once it reaches the right color
Use immediately or add the gumbo ingredients right away