MAKE CHOCOLATE MIXTURE: Melt chocolate chips in a medium or small saucepan over low heat, stirring until smooth. Stir in 1 cup cream and 1 cup (85 grams) grated coconut. Pour into a large bowl and let cool to room temperature. Whisk egg yolks into cooled chocolate mixture.
WHIP CREAM: Using an electric hand mixer or immersion blender, in a separate bowl, beat the chilled whipping cream until soft peaks form. Set aside (place bowl in fridge if possible).
BEAT EGG WHITES: Clean and dry the beaters, then in a separate small bowl, beat egg whites until stiff peaks form, but not dry.
COMPLETE THE MOUSSE AND FREEZE: Gently fold whipped cream into the melted chocolate mixture in 2-3 stages. Then gently fold in whipped whites. Pour mousse mixture into a 10 inch (25 cm) springform pan (9 inch/23 cm will work too) with 2 inch/5 cm sides. Cover with plastic wrap and freeze at least 6 hours or overnight.
MAKE CARAMEL SAUCE: Stir sugar and water over low heat in a medium saucepan until it dissolves (about 5-7 minutes). Increase heat to medium heat and gently boil WITHOUT STIRRING until the syrup turns a deep amber color (about 8-9 minutes). Carefully add whipping cream (it will bubble vigorously) and stir until smooth. Remove from heat. Stir in butter and vanilla until smooth. If making a day ahead (or more), cover and refrigerate, then when ready to use, heat on low, stirring frequently until warm. Put sauce in a gravy or coffee thermos if desired to keep warm.
TO SERVE: Place mousse in fridge for 30 minutes before serving to soften slightly. Run a sharp knife around the sides, the release the sides of the spring form pan. Place mousse (with bottom of spring form pan) on a serving plate. Sprinkle on coconut for garnish (I like to toast coconut first). Ladle a bit of warm caramel sauce onto plates. Slice mousse into thin wedges (it's very rich so keep slices thin!). Drizzle on a bit more sauce you like. Dig in!