1. Carefully remove rind from lemons using a vegetable peeler, making sure to avoid white pith. Thinly slice rind from one lemon, and place in a Bundt pan. Add 2 cups water, ginger, apricots, and cranberries, and freeze for 4 1/2 hours or until firm.
2. Place rinds from remaining 5 lemons and sugar in a medium bowl. Muddle rinds and sugar together using a muddler or wooden spoon, working sugar into rinds to release their oils. Cover and let sugar mixture stand at room temperature 1 1/2 hours.
3. Add juice to rind mixture; stir until sugar dissolves. Strain rind mixture through a sieve into a bowl; discard rinds. Stir in gin and blood orange liqueur; cover and chill at least 3 hours.
4. Unmold ice ring by dipping bottom half of Bundt pan into several inches of warm water for 5 to 10 seconds to loosen; repeat as necessary to release. Invert ice ring into a large bowl or punch bowl. Pour gin mixture over ice ring. Gradually add prosecco. Garnish with rosemary, if desired.