For Mousse: =========== Heat sugar and water in heavy saucepan over medium-low heat until sugar dissolves, stirring occasionally and brushing down any crystals from sides of pan with brush dipped in cold water. Increase heat and boil until mixture registers 120ºC (soft ball stage) on a candy thermometer. Meanwhile, beat egg whites and cream of tartar until soft peaks form. Slowly pour in hot syrup, beating until mixture is cool, about 5 minutes Gently fold in whipped cream, cocoa, melted chocolate and espresso. Cover and refrigerate for 1 hour.