Mousse: Melt chocolate chips in heavy medium saucepan over very low heat, stirring until smooth. Add 1 cup heavy cream and coconut and stir until smooth
Pour in a large bowl and cool to room temperature. Whisk egg yolks into chocolate mixture. Using mixer, whip 1 cup chilled cream in medium bowl until soft peaks form
Fold into chocolate mixture. Beat egg whites until stiff, not dry. Gently fold into chocolate mixture
Pour mixture into a 10-inch diameter springform pan with 2-inch sides. Cover and freeze at least 6 hours. Can be made two days ahead of planned serving
Caramel Sauce: Cook sugar and water in medium saucepan over low heat, stirring until sugar dissolves. Increase heat and boil without stirring until syrup turns a caramel color
Add cream (mixture will bubble vigorously) and stir until smooth. Remove from heat. Add butter and vanilla and stir until smooth
Caramel sauce can be prepared one day ahead. Cover sauce and refrigerate. Rewarm over low heat, stirring
Place mousse in refrigerator 30 minutes before serving to soften slightly. Run small sharp knife around cake pan sides to loosen
Release pan sides. Cut mousse in wedges. Ladle warm caramel sauce onto plates. Place mousse wedges on top of sauce. Garnish with coconut and whipped cream.
