Cut the tops off the oranges. Scoop out all of the pulp and juice from the oranges, reserving about 1/4 cup pulp and juice. Set orange shells aside.
In a large bowl, mix sherbet and ice cream together. Add liqueur and the orange pulp and juice and stir to combine. Freeze until just firm. Spoon mixture into the orange shells, packing it down. Freeze for 2 hours. Serve garnished with mint leaves.