Saute the shallots and mushrooms in 2 tablespoons of butter till lightly browned. Add stock add wine and reduce by half.
Add cream and vanilla bean and reduce again to a light sauce consistency. Strain. Scrape the soft center of the vanilla bean into the strained sauce. Correct seasoning with drops of lemon juice, salt and pepper. Whisk in remaining butter in bits. Hold the sauce in a warm water bath until serving time (up to 2 hours).