Sauté 3 ounces (75 grams) sliced mushrooms in butter until lightly brown. Sprinkle the mushrooms with 1 heaping tablespoon (20 milliliters) finely chopped shallots about 2 minutes before they are done. When the mushrooms are lightly browned and no liquid remains in the bottom of the sauté pan, deglaze the pan with 6 tablespoons (90 milliliters) white wine and 2 tablespoons (30 milliliters) Cognac. Quickly reduce the wine-Cognac mixture by half. Add 6 tablespoons (90 milliliters) tomato sauce (Tomatoes; optional) and 6 tablespoons (90 milliliters) demi-glace. (If the tomato sauce is omitted, use ¾ cup/185 milliliters demi-glace.) Bring the sauce to a simmer and skim off any fat or scum that floats to the top. Whisk in 1½ ounces (45 grams) butter. Finish the sauce with 1 teaspoon (5 milliliters) chopped chervil and 1 teaspoon (5 milliliters) chopped tarragon.