Melt 2-1/2 tablespoons butter in a saucepan, stir in 3 tablespoons flour, and gradually add 1/2 cup chicken stock, stirring constantly. Cook for a few minutes, stirring and slowly add 1/2 cup heavy cream, blending It into the mixture thoroughly.
Remove the sauce from the heat and add 2 cups crabmeat, 1/2 teaspoon chopped tarragon, 2 teaspoon chopped parsley, 3 tablespoons chopped sauteed mushrooms and 1/2 teaspoon salt. Spread the mixture on a platter to cool, form it into small balls and brown the balls lightly in hot deep fat. Pierce the bouchees with wooden picks and serve them hot to accompany cocktails.