How to Make a Roux (and a Smooth White Sauce)
Cook flour in melted butter for a minute, then whisk in the liquid gradually. It thickens sauces, gravies and casseroles without lumps.
A roux is equal parts fat and flour cooked together. It's how gravy, cheese sauce, chowder and from-scratch casserole sauces get thick and silky, and it's the base canned cream soups are made from.
Cooking the flour in fat first coats every grain, so it can't clump when liquid goes in, and it removes the raw, pasty flavor. The longer you cook it, the darker and nuttier it gets, but the less it thickens.
How to do it
Melt the fat
Melt butter (or heat oil) over medium heat. Use about 1 tablespoon of fat and 1 tablespoon of flour for every cup of liquid you want lightly thickened.
Cook the flour
Sprinkle in the flour and stir for 1 to 2 minutes, until it smells toasty and looks like wet sand. For a white sauce, stop before it colors.
Add liquid gradually
Pour in about a third of the liquid while whisking constantly until smooth, then add the rest in two more additions.
Simmer to thicken
Bring it to a gentle simmer and whisk for 2 to 3 minutes. A roux reaches full thickness only once it bubbles.
Common mistakes
- Dumping in all the liquid at once, which makes lumps.
- Undercooking the flour, which leaves a raw, pasty taste.
- Judging thickness before the sauce simmers; it thickens a lot once it bubbles.
