HOW TO MAKE WHITE SAUCE
White sauces are made basically of a white stock, coming from chicken, fish, or veal, which is further thickened with a roux. Some sauces call for additional ingredients, like milk, and some aromatic vegetables (mirepoix, mushrooms). The thickness of the white sauce will be dependent on how much roux is added. Important point to bear in mind is that white sauces are easily burned and they can become discolored by aluminium pans. To get the best white sauce possible use therefore a good flat-bottomed pan (I mean really flat and not diagonally skewed as some pans are) that is made of other material than aluminium. The heat distribution from the stove to the pan has to be uniform, so no spots of high heat can destroy the sauce. If you have that covered, then let's get ready to make the white sauce.
A starter recipe is as simple as it can get: use 4 dl/13.3 fl oz of a white stock or milk and about the same amount of roux. How to make roux (flour and fat) is covered in another article on in our HOW TO section so go there if you need. Make a roux that is white or blond, otherwise the sauce will not be white! For additional flavor, you can also throw in some aromatic ingredients, e.g. mirepoix or some onions or onion-family members that have been finely chopped for maximal and quick flavor extraction. Once you've prepared all the ingredients, start preparing the sauce.
First, if you use any aromatic vegetables or mushrooms, start to sauté them in a little amount of fat, just for a few minutes on moderate heat so they release their flavor. You can also use some meat or fish trimmings here but just make sure so you don't brown them, just cook them. Once the aromatic ingredients are sweated, add the roux and let it heat up. If you don't want to pre-make a roux you can do it right away in the pan where the aromatics are - just add the right amount of flour and fat and heat everything up and cook to a light blond color (should take a few minutes). Just make sure so the flour is evenly distributed without any lumps.
Then, start adding the stock (or milk) to the pan. Make sure so that the stock is colder than the roux, it can be cold from the refrigerator or room-tempered, or even slightly hot, as long as its temperature doesn't exceed the temperature of the roux. Also, make sure to add the stock a little at a time, whisking frequently so the sauce is always kept smooth.
Next step is to season the sauce with whatever the recipe calls for. Some white sauces, like bechamel, need some nutmeg and cheese, while bohemienne sauce uses tarragon. Simply add the proper seasoning and simmer the sauce until the flavor has been developed. Also, you need to simmer for long enough time to remove the starchy feel of the roux, which could take about half an hour. When you simmer the sauce, remember to stir it from time to time, making sure so that the bottom of the pan is free from any scorched sauce. This is especially important with sauces that use milk, since milk proteins have tendency to easily scorch. Cook the sauce until it loses its stickiness and the starchy feel. At last, strain the sauce to remove any heavy layers or gluey textures within it. Serve immediately. The sauce should be white, it should be glossy, and it should flow without any stickiness felt in your mouth. The flavor should of course reflect the ingredients you've been using, and it shouldn't taste burned. It should be thick so it can coat the back of the spoon, yet it should be flowing easily. In other words, it should be perfect!