HOW TO MAKE BEURRE BLANC OR BEURRE ROUGE
Beurre blanc is a sauce based on butter (beurre) and reduction of white (blanc) wine or other "white" ingredients, often shallots. Beurre rouge makes use of a reduction of red wine. Beurre blanc can be used to make other sauces, in which it serves as a base. Ingredients like vinegar, aromatic citrus fruits, herbs of all kinds, and a variety of spices and seasoning can be included in beurre blanc or rouge.
For the best sauce use usalted or just lightly salted butter so you have control over the salt content of your sauce. Also, use pans that don't discolor the sauce; stainless steel is good. And of course, since it is a sauce, you expect it to carry lots of nice flavors and freshness, therefore use the best and fresh ingredients in it. If you want to stabilize beurre blanc emulsion then you can also add some reduced lightly yellowed heavy cream (the color becomes yellowish when you reduce the cream), however be careful with it since you don't want to cover the taste of butter too much. After all, beurre blanc is a butter sauce! Once you've made the sauce then keep it hot before you serve it, but don't wait too long with getting it out to the plates.
Making beurre blanc is simple and it opens lots of possible variations of flavors, all according to the dish you are making and to your palate's desires. Basic ingredients for 0.5 l/1 pint of beurre blanc include:
350 g/12 oz butter cut into smaller cubes
120 mL/4 fl oz white wine, or red wine (for beurre rouge), reduced along with
40 mL/over 2 tbsp vinegar, plus shallots and possibly other spices (peppercorns, garlic, herbs, saffron)
salt, white pepper, lemon juice - all to taste
And if you want to stabilize the emulsion for a longer while - reduction (yellow colored) of 3 tbsp of heavy cream
Making the beurre blanc:
Make the reduction of the basic ingredients (wine, vinegar, aromatics) so the liquid becomes like a syrup (a sec). Do it on a hot stove in a sauce pan. Then, reduce the heat to low and start throwing in the pieces of butter and gradually whisking them into the reduction. You can also swirl the pan continuously if you prefer it instead of whisking. The goal now is to get a creamy texture. If you get an oily sauce then you have too much heat in the pan, but don't panic - just remove the pan from the heat on a cool place and continue to add butter and whisking. The desired creamy texture should appear, and so then put the pan back on the low heat. (On the other extreme, the pan can get too cold and the butter will not incorporate fast enough into the sauce, and the remedy for this is of course to increase the heat.)
As all butter is incorporated into the beurre blanc, make the final flavor and seasoning adjustments. That's it! Now you can strain the beurre blanc through a fine sieve, but if you want to leave the aromatics in there then go ahead. When straining, you should do it quickly and pour the sauce into a preheated pan/bowl so it doesn't get destroyed too quickly. Then, keep it warm and serve as soon as possible.
Beurre blanc should taste butter. It is a butter sauce flavored with a few other ingredients. The texture should be creamy and the look should be fairly shiny. The fine line in beurre blanc is to find the proper amount of butter (above quantities should work fine), because if you have too much of it then the sauce will be too greasy, and too little butter will make beurre blanc too thin.