Techniques
What is a roux?
The short answer. A roux is flour cooked in fat, usually butter, used to thicken sauces and gravies.
Equal parts fat and flour by weight is the classic ratio. Cook the paste for about a minute so the raw flour taste cooks off, then whisk in liquid gradually so lumps cannot form.
The longer a roux cooks, the darker and nuttier it gets, and the less thickening power it has. A pale roux is used for white sauces and country gravy.
Where it shows up in our recipes
Question
Why is my roux lumpy?
The liquid went in too fast or was too cold for the hot roux. Add it a little at a time while whisking.