Roux ingredients in a pot with a wooden spoon
The Ingredient Switch You Can Make For Flour When Making Roux
Roux is a versatile flour-and-fat paste that works as a base for gravy, béchamel, and more. If you don’t have flour on hand, there are a few substitutes you can choose from.
Cornstarch is the simplest replacement for flour. It’s neutral in flavor, easy to use, and creates a roux with the same thickening power and consistency as one made with flour.
Although flour can be sprinkled directly into the pan with the fat and whisked in to form a roux, cornstarch needs to be made into a slurry first before it's mixed in.
Add cornstarch to a room-temperature liquid, such as water or stock, in a 1:2 ratio. Use a fork to whisk the mixture vigorously and dissolve the starch completely.
Add the slurry to the warm saucepan full of fat, whether it be butter or something else. Adding the cooler slurry to the hot pan gelatinizes the starch and helps it thicken.
A cornstarch slurry doesn't toast or brown like flour does, so for a darker roux, you need to use butter and carefully brown it first before adding the slurry.
You can also try chickpea flour, potato starch, arrowroot powder, or tapioca starch in place of flour. Chickpea flour in particular behaves similarly to wheat flour.