Cover until shallots soften and most of the mushroom liquid has cooked off, about 10 minutes.

Place the fillets in the skillet, spooning the mushroom liquid over the top.

When they are heated through, strain and add the mushroom liquid.

Add the vinegar and wine to the mushroom liquid and cook for one minute.

Place over high heat and boil until the mushroom liquid evaporates; do not let mushrooms brown.

Add the mushroom liquid and chocolate and bring the mixture to a boil.

In same skillet, place mushrooms, garlic and mushroom liquid.

Simmer until the mushroom liquid has evaporated, about 8 minutes.

Add a little pasta water or mushroom liquid to loosen it.

Add some mushroom liquid if mixture has become too dry.