Melt butter (or fat) in a saucepan and whisk in flour until smooth. Allow it to bubble for at least 1 minute while mixing.
For a blonde roux, allow it to cook a minute or so.
For a dark roux, cook the flour/fat mixture longer while whisking, until it reaches a golden dark caramel color.
Add cold liquid a little at a time while whisking until smooth after each addition.
Add remaining liquid and seasonings, simmer a couple of minutes.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)