1Put the broth and porcini into a microwave-proof bowl, microwave on hi for 1-2 minutes or until boiling. Let sit until mushrooms soften up a bit. (About ½ hour… I do this first and then get the other stuff together.)
After the mushrooms are softened, scoop them out of the broth, drain and chop coarsely, saving the broth. Set aside. Strain broth through cheesecloth or a coffee filter (this will keep the sand out of the sauce) and set the broth aside.
Melt the butter over medium-high, sauté the shallots and garlic until softened and golden, but not burned (5 or so minutes). Add the reserved mushrooms and sauté for another 5 minutes. Deglaze the pan with the cognac (watch out, it may flare up).
Add the reserved broth and simmer for about 30 minutes (to reduce the liquid), add the cream, tarragon and nutmeg and simmer for another 10-15 minutes until the sauce thickens (fresh cream will not curdle).
Stir in the parsely. Add salt and pepper to taste (taste it first, the reduced broth should already have given you enough salt).