How to Make It
Let 2 pints sorbet stand at room temperature until soft enough to be easily scooped, about 10 minutes. Arrange lemon and lime slices around sides of a small (8-cup) metal tube or Bundt pan or freezer-safe bowl. Scoop softened sorbet into pan, packing citrus slices against sides; smooth top. Cover with plastic wrap and freeze until firm, about 5 hours.
When ready to serve punch, pour gin into a large chilled punch bowl, and add remaining 1 pint sorbet. Mash sorbet with a spoon to incorporate with gin; add frozen citrus ring to bowl. Gently pour Champagne around inside of bowl; stir gently to combine with gin mixture. Garnish with maraschino cherries. Place ladle in bowl, and allow guests to serve themselves.