A traditional demi-glace recipe is made by combining a mixture of half basic brown sauce and half brown stock (such as beef stock) and then simmering until it's reduced by half.
In this shortcut recipe, instead of making the stock from scratch, store-bought stock or broth is used. It won't have the same body as a homemade demi-glace, but it'll save you about 8 hours.
Use the best quality stock or broth you can find and stick to the low-sodium, reduced-salt (or even no-salt) varieties. Reducing concentrates the saltiness, and you don't want your finished sauce to taste like a salt-lick.
You'll need some cheesecloth for straining the sauce and also for making the sachet d'épices, as well as some cooking twine for tying it up.
