Dark Roux

In a heavy-bottom saucepan, heat oil over medium heat until very hot. Whisk in the flour, a little at a time and cook, whisking constantly, until roux becomes smooth and thick. Continue to cook, constantly stirring with a spoon and reaching all over bottom of pan, until the roux darkens to a rich brown nutty color, about 25 minutes. (The time may vary according to your cooktop.)