Preheat broiler; grease rack in broiler pan. Place salmon steaks on rack; broil 8-10 minutes, until fish flakes easily when tested with fork. Place salmon on platter and keep warm.
Saute mushrooms in 2 T. butter and set aside.
In 1 quart saucepan over medium-high heat, bring wine, tarragon, shallot, vinegar, chervil, and pepper to a boil; boil for 5 minutes or until liquid is reduce to about 2 tablespoons. Reduce heat to medium and add remaining 8 tablespoons butter, 1 tablespoon at a time, beating constantly with a wire whisk until butter is melted and mixture thickens slightly. Remove saucepan from heat and stir in whipping cream. Add sauteed mushrooms to the sauce. Salt to taste.
Serve salmon steaks with sauce and garnish with parsley.