In a saucepan, soften shallots in butter. Season with salt and pepper. Sprinkle with flour and cook for about 1 minute, stirring constantly. Add Marsala wine and bring to a boil, stirring with a whisk. Add veal stock, maple syrup, mushrooms, and reserved soaking water. Bring to a boil and reduce by three quarters or until sauce begins to be slightly syrupy, about 15 minutes. Add cream and heat through. If necessary, reduce again to get about 430 ml (1 ¾ cups) of sauce. Adjust seasoning.