Sauté the mushrooms and shallots in butter in a medium-sized skillet over medium-high heat for about 4 minutes.
Reduce the heat slightly and stir in the flour. Blend the flour well, breaking up any lumps that develop.
Remove the skillet from the heat and gradually stir in the stock and the cream, blending well with the flour.
Add the tarragon, wine and salt and pepper to taste. Let the sauce bubble gently for a few minutes until it reaches the desired consistency.
If it's too thick, add a bit more broth. If it's too thin, cook down a little more.
If you'd like to use this recipe for red meats, substitute 1 cup of beef stock for the chicken stock.
Season with snipped fresh thyme and rosemary in place of the tarragon - about a tablespoon each. Add a dash of Worcestershire.