Melt chocolate and butter together in microwave or in a double boiler. Whip eggs yolks, sugar, vanilla and salt vigorously together for about 2 minutes, until well combined. Combine melted chocolate with the egg mixture. Whip egg whites until soft peaks form. Sprinkle flour over the chocolate-egg mixture and add the egg whites. Gently fold everything together until well combined. Butter and flour four ramekins and spoon the mixture into the ramekins. Bake at 450F oven for about 8 minutes, until the top is set. Serve warm or at room temperature with berries and whipped cream. Serves 4.