How exactly do I use demi-glace? I know it's something used to enrich sauces and such, but since it is so time-consuming to make and the little jars of it are very expensive, I never really gave it that much thought. Now a friend has moved out of state and given me her stash of homemade demi-glace cubes (she kept them in the freezer). So, um, what exactly do I do with them? Directions more specific that "throw some in a sauce for steak" would be appreciated, as I have no idea how much of this stuff to use relative to other ingredients. Thanks.