This classic sauce, once made with white wine, is made in a classic kitchen by adding demi-glace or glace de viande to a red wine reduction and finishing the sauce with cubes of beef marrow. The marrow can be replaced with a swirl of butter. The red wine is best reduced along with the demi-glace or glace de viande so the proteins take out some of the tannin. Best of all is a Bordelaise sauce made starting with red wine stock (simply make a veal stock or other stock using red wine instead of water). As for all brown sauces, the thickness of the sauce is largely a matter of taste. If red wine stock is used, very little reduction will be required to cook off the acid and tannin in the wine and the sauce can be left almost like a rich broth, served around a good steak in a soup plate, or it can be reduced and thickened with butter, perhaps in conjunction with hydrocolloids, emulsifiers, and emulsion stabilizers.