Preheat oven to 350°.
Coat an 8-inch springform pan with cooking spray; line bottom of pan with parchment or wax paper. Wrap outside of pan with aluminum foil.
Place 3/4 cup sugar and eggs in a bowl; beat with a mixer at high speed 7 minutes.
Combine cornstarch and cocoa in a small bowl; set aside. Place juice, liqueur, water, salt, and chocolate in a small glass bowl; microwave at high 1 minute or until almost melted, stirring every 20 seconds until smooth. Add cornstarch mixture; whisk until smooth.
Gently stir one-fourth of egg mixture into chocolate mixture; gently fold into remaining egg mixture. Scrape batter into prepared pan. Place pan in a 13 x 9-inch baking pan; add hot water to larger pan to a depth of 1 inch. Bake at 350º for 20 minutes or until top is set. Remove cake pan from water; cool 5 minutes on a wire rack. Loosen cake from sides of pan using a narrow metal spatula; cool to room temperature. Cover and chill at least 4 hours or overnight. Garnish with powdered sugar and rind just before serving, if desired.