Melt butter in a small, heavy pan over low heat. (For most recipes, three tablespoons of butter and three tablespoons of flour are the right amount.) When the butter is melted, whisk in an equal amount of flour, continuing to whisk until the mixture is smooth. Allow the mixture to bubble slowly, whisking constantly so that it does not burn. Keep heat very low throughout the cooking process. Cook for about 2 to 3 minutes, or until it is pale golden in appearance. At this point, it will have lost some of its raw flour taste.
Some roux are cooked longer than this typical white roux. The longer you cook it, the more flavor it has.
Slightly darker, blond roux is darker and thinner in texture than a white roux, while brown roux is more pungent and nutty in flavor. A blond roux cooks for approximately 6 minutes. Brown roux, which has much less thickening power than white roux, is used primarily to thicken classic brown sauces and gravies.