Step 1

Melt the butter. Melt 4 tablespoons unsalted butter in a large regular or cast iron skillet over medium-low heat.

Step 2

Add the flour. As soon as the butter is melted, add 1/2 cup all-purpose flour and immediately stir with a wooden spoon in a figure-eight motion until the flour has completely absorbed all of the butter, 30 seconds to 1 minute. There should be no dry pockets of flour left in the mixture.

Step 3

Cook the flour. Continue cooking, stirring constantly, until the mixture is smooth, slightly thickened, and small bubbles begin forming, 30 seconds to 1 minute. The roux should smell nutty and there should be no unincorporated flour left. If any lumps of flour remain, break them up with the spoon.

Step 4

Cook to the desired color. At this point, you have a white roux that is perfect for using in light sauces such as béchamel. For a blonde roux (which can be used interchangeably with a white roux but has a slightly nutty flavor), continue cooking over medium-low heat, stirring constantly, until the roux is a pale golden color, 3 to 4 minutes. For a brown roux (most commonly used to thicken gumbo), cook until the roux is dark brown and very fragrant, 10 to 12 minutes.