Melt the butter in a sauteuse. Add the mushrooms. Saute the mushrooms over a relatively high flame for a few minutes. Add the chopped shallots, turn down the flame and allow them to sweat for several minutes. (Mushrooms and shallots sweated down constitutes a duxelles - a basic French culinary invention.) Quench with white wine, and add the Sauce Espagnole, tomatoes and garlic to the pan. Adjust for seasoning. Bring the contents of the pan a slow boil. Simmer for 15-20 minutes. Sprinkle in chervil and tarragon, then cut off the heat.