This dessert sounds exotic but it is quite easy to make from softened sorbet.
Spread lemon sorbet into bottom and up sides of a 10-cup fluted pudding mold. Freeze until firm, about 1 hour. Fill bowl with champagne sorbet, and smooth top of bombe. Cover with plastic wrap, and freeze overnight (or up to 1 week).
Dip mold in hot water to make it easier to unmold. Invert onto a cake stand, and remove mold. Serve, or freeze 2 hours more to firm the outside before serving.