In a saucepan, combine butter, lemon juice and parsley until melted. Set aside. In a large stockpot, add beer and salt. Cover and boil. Add mussels, chopped red onion and chopped garlic and steam until the mussels open. To reserve juice, add 35% whipping cream and reduce to 1 1/2 cups. Add chopped parsley mixture and pour over mussels.