Use a spoon to scrape the seeds out of the melon. Peel melon and cut into pieces. Peel the kiwis and cut them into pieces. Wash the mint and dab dry. Put 4 twigs aside. Cut the rest into fine strips.
Finely puree melon, kiwi and buttermilk with sugar. Stir in mint. Pour the drink immediately into 4 glasses (250 ml each), fill up with crushed ice and decorate with set aside mint sprigs.
Serve immediately, as the kiwis make the drink bitter if left standing for a long time.