Heat together butter, peanut oil, lemon juice & rosemary in skillet until boiling. Add fish: cook briefly until fish turns opaque on first side. Turn & cook briefly on reverse side. Push fillets to one side of skillet; add remaining ingredients, stirring to blend. Return fillets to center of pan; cover, reduce heat, & poach for 6 minutes, basting often with sauce. Remove fish from pan to heated platter; keep warm. Continue cooking sauce to reduce slightly. Spoon sauce over hot fish to serve.