For the ice cream bombe:
1) Freeze a 20cm bowl. When it's cold, place the mango sorbet in the bowl and press it against the sides. Use a 16cm bowl the same shape as the 20cm bowl (from a set of nesting bowls), cover it with cling film and press it into the sorbet to make the layer even. Freeze the sorbet for 30 minutes or until firm.
2) Remove the 16cm bowl. Spread an even layer of softened raspberry sorbet on top of the mango sorbet (a 11cm nesting bowl wrapped in cling film helps with this) and freeze for another 30 minutes or until firm.
3) Remove the 11cm bowl. Finally, spoon in enough softened strawberry ice cream to fill the bowl. Freeze until hard.
4) To unmould, dip the bowl up to the rim in warm water. Run a knife around the edge to loosen the bombe and unmould upside down onto a flat plate. You may need to run a flexible metal spatula along the edge of the bombe to release it. Freeze until ready.
5) Serve cut in wedges.
For the mango sorbet:
1) Place the sugar and 120ml of water in a small saucepan and cook until the sugar dissolves. Set aside.
2) Place the mangoes in a food processor fitted with the steel blade and puree. You should have about 1.1 litre of puree. If you want a smoother sorbet, you can process the puree through a food mill fitted with a medium blade.
3) Combine the mango, sugar syrup, orange juice, and salt and refrigerate until cold. Freeze in an ice cream machine according to the manufacturer's directions (the sorbet will be soft).
4) Serve directly from the ice cream machine or use as directed for the bombe.