Soften the sorbet for about 15 seconds in a microwave oven.
Working on parchment-lined cookie sheet, use a spatula to pack sorbet into the cutters. Smooth tops with spatula. Lift off rings.
Put the rounds in the freezer to set, about 1 hour.
Stack tiers onto parchment-lined cookie sheets; return to freezer. Just before serving, slide the cakes onto plates; garnish with berries or other fruit. Cakes can be made up to a day in advance.