How to Make It
Combine mint leaves, 1½ cups water, and sugar in a medium saucepan. Bring to a simmer and cook, stirring often, until sugar is dissolved, about 4 minutes. Cover pan, remove from heat, and steep 10 to 15 minutes. Pour mixture through a fine-mesh strainer, discarding solids, and let cool completely.
Stir together gin, lime juice, lemon juice, and mint syrup in a punch bowl. Top with champagne. Serve punch over ice, garnished with mint sprigs and lime wheels.
Tip: Mix the mint syrup, gin, and citrus juices together at home and pack in a plastic container. Pop the champagne and mix the punch when the last guest arrives.