Pour the boiling water over the mushrooms and let steep for 10 minutes. Stir occasionally.

Place the mushrooms and liquid in a blender and puree until smooth.

Place the pureed mushrooms in a fine mesh sieve over a small mixing bowl.

Use a rubber spatula to force the mushrooms through the sieve.

You will have about 1 cup of thick mushroom broth and probably about 1/3 cup of mushrooms that cannot be forced through the sieve. Discard those mushrooms and set the mushroom broth aside.

Place 1 tablespoon of the butter in a medium skillet over medium high heat.

When the butter begins to foam, add the shallots.

Cook for about 4 minutes. Stir frequently.

Add the white wine and adjust the heat until the sauce is simmering.

Cook until almost all of the wine is reduced.

Add the mushroom broth, mustard, salt, pepper and the remaining 1 tablespoon butter.

Heat through until the butter is melted and the sauce blended.

Serve.