Bake pie shell. Heat chocolate until melted; cool 10 minutes. Beat cheese, 1/3c brown sugar, the coffee, salt and vanilla on low speed until smooth. Add egg yolks and chocolate. Beat on high speed until smooth. Beat egg whites on high speed until soft peaks form. Beat in 1/4c brown sugar until stiff peaks form. Fold egg whites into chocolate mixture. Reserve 1/2c of the whipped cream; fold remaining whipped cream into chocolate mixture. Pour into shell. Mound remaining whipped cream on pie. Garnish with grated chocolate if desired. Cover; freeze at least 8 hours. Remove from freezer 20 minutes before serving.