Okay, I reduced the stock by one half, but the resulting product is still quite liquid -- not very gelatinous, as the Pepin photos suggest it should be. Does it matter? I don't know. But I kind of liked the idea of being able to make and freeze gelatinous cubes of demi glace for my discretional use. Not sure what I'm going to do with all this stuff.
Dinner party at my house, maybe?