Roux, a combination of flour and oil or butter, is often used as a base for many sauces, to thicken stews, make gravy, and add a nutty, toasted flavour to dishes. If you're short on time, make roux in the microwave.
Mix equal parts flour and some kind of fat in a microwave-safe dish, then stick in the microwave for a short time, stir and repeat until it looks right. Cook's Illustrated (paywall) recommends olive oil rather than butter, because the oil requires less stirring. Two tablespoons of oil and two tablespoons of flour will turn into 1/4 cup of roux. Microwave for a minute and a half and stir. Then put back in the microwave for 45 seconds, stir, microwave again for 45 seconds and give it a final stir. If you want a darker roux, continue alternating microwaving and stirring in 15-second increments.
The Newlyweds blog microwaves in three-minute increments and offers step-by-step photos.
Shrimp and Okra Gumbo [Newlyweds]