* One oz. = 2/3 cup.
Suggested mushrooms are cepes, porcini, Steinpilze or boletes marketed as "Chilean dried mushrooms."
Combine mushrooms in a bowl with 4 cups very warm water. Push them under the surface, weight them with a saucer, and let them soak overnight or for at least 6 hours, until they are very soft. Stir them occasionally.
Lift mushrooms from the liquid with a slotted spoon (save the liquid) and chop them fine, saving as much juice as possible. Combine them with the remaining 2 cups water in a saucepan, bring them to a simmer, and simmer them, covered, for 20 minutes.
Meanwhile, to clear the soaking liquid of grit, pour it carefully into a bowl, leaving behind the sediment - this is certain to be sandy. Let the liquid settle again and again pour it off; repeat, if necessary, to be sure any grit has been left behind.
Pour the simmered mushrooms and their liquid into a sieve set over a bowl and lined with fine nylon net or two layers of dampened cheesecloth. Press hard on the mushrooms to extract all possible liquid; discard the debris. Let this second batch of liquid settle, then decant it as described for the soaking liquid; repeat if necessary.
Combine the two batches of liquid with the shallots, peppercorns, mace and bay leaf in a saucepan. Bring the liquid to a boil over medium-high heat and simmer it briskly, uncovered, until it has reduced to 2 cups.
Strain out the solids and let the concentrated liquid settle for one last time - we're still on the track of any sand that may remain. Decant the cooled essence, then freeze it in an ice-cube tray. Remove the cubes from the tray and store them in an airtight freezer container. Keeps for up to a year in the freezer.
Makes: 16 cubes, about 2 tb. each.