Roux cooked in the microwave certainly isn't traditional, as there were no microwaves in the 18th and 19th centuries. But if there were, you can bet that even some Cajun traditionalists would have made use of the microwave on occasion to make their roux!
See the following links to learn more about the history of roux, and about making traditional and oven roux:
Yield: About 1 Cup Roux
- 1 cup all-purpose flour
- 1 cup cooking oil
Whisk flour and oil together until smooth and lump-free in a 1-quart Pyrex (or other microwavable) measuring cup or bowl--don't use plastic!
Place the measuring cup in the center of the microwave oven and cook on high for 10 to 30 minutes, removing cup and whisking to mix well every 2 minutes. Use a pot holder, as the Pyrex cup will be very hot!
Cook until the desired color is reached: it takes 20 minutes to make the medium (or peanut butter colored) roux in the microwave --see photo.
A darker roux (one that has been cooked longer) will have more flavor, but will have less thickening power. This is because flour loses its ability to thicken the longer it is cooked.
The roux seems to be cooking very fast or getting very dark, turn the heat down. Above all, stir almost constantly--at least every 15 seconds; with each stir the roux gets just a bit more brown.
When the roux reaches the desired color, you may proceed with a recipe, adding the holy trinity of onion, celery, and bell pepper, and whatever main ingredient you are using, plus seasonings and water.
Make Ahead Roux
If you are making the roux ahead to keep as needed, transfer it to a large glass or plastic bowl to stop the cooking process, stirring occasionally as it cools down. Roux can be kept, covered, in the refrigerator for two months, or in the freezer for six months.
If freezing the roux, place 1 tablespoon of the roux in each section of an ice cube tray and, when firm, transfer to a freezer bag. When a recipe calls for 1/2 cup roux, pop out 8 cubes (8 tablespoons, or 1/2 cup). You may also use a cube or two at a time if your stew, soup or sauce needs a bit of thickening.
3 cups oil + 3 cups flour = 3 2/3 cups roux
1 cup oil + 1 cup flour = 1 cup plus 3 tablespoons roux
If a recipe calls for making a roux with 1/2 cup oil and 1/2 cup flour, use 1/2 cup of prepared roux, or a quantity of prepared roux equivalent to the amount of flour called for in the recipe.
To thicken 6 to 8 cups of liquid for a gumbo, soup or other dish, use 1 cup prepared roux, or start with 1 cup flour and 1 cup fat.
What to Look for When Cooking Roux
After a few minutes the roux is likely to become foamy and remain so for several minutes. After about 10 minutes the roux will begin to turn dark and will develop a nutlike fragrance. After about 20 minutes the roux will start to cook faster and must be watched more carefully so it doesn't burn. Lower the heat if necessary--a burned roux is only fit for the garbage.
If the roux starts to smoke, lower the heat or turn the off for a bit to allow the roux to cool down. If the oil gets hotter than the point at which it starts to smoke, it may negatively affect the taste.