Making a Roux
The roux is generally made of equal parts of flour and oil. The color comes from the length of cooking. For a dark sauce, cook the flour until it turns the color of peanut butter. But for a white sauce, stop much sooner, before it browns.
You stop the roux browning when you add liquid to the roux. The liquid might be wine, broth, water, or liquid you ladle out of a pot of stew. When you add the liquid, it will hiss and steam for a minute, and begin to thicken immediately. Add liquid until it is the consistency you want, or dump the roux back into the cooking pot when thickening the liquid for stew or pot roast.
A recipe will normally tell you how much flour and oil you need. To make a sauce for a few people to put over their steaks, you might use three tablespoons of each, 1/4 cup of wine, some parsley and tarragon, and a few butter pats to finish the sauce. If instead of the oil you use part oil and part butter, you will gain some flavor from the butter, and the oil will help avoid scorching the butter.
Sometimes you will make a roux after sautéing a mirepoix, a mixture of chopped carrots, onion, and celery. This is a frequent and very flavorful beginning to many soups and stews. It’s one reason why I keep those three vegetables on hand as staples.
Anyway, experiment and enjoy. Don’t get distracted by the phone, changing the baby, or breaking up the cat fight in the living room. A roux doesn’t take long to make, and it doesn’t take long to burn. But it’s worth the few minutes of attention because of the flavor and quality it adds to the food.