Note: Although you can stir the roux with a metal spoon, I highly discourage it. A spoon collects liquid and makes it easier to splash out of the pan and burn you. By contrast, a whisk allows the roux to pass through it and reduces the possibility of splashing, as well as getting into the sides of the pan. It’s important that you whisk the entire bottom of the pan when cooking roux; if you miss a spot the flour can stick and burn, which will give the entire pot an acrid flavor. Remember to stir slowly—roux has been called “Cajun napalm” because, if it gets on your skin, it sticks and burns. And beware, roux will catch on fire if left unattended.