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 240 F (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.