Line the base and sides of the cake tin with greaseproof paper, leaving an overhand so you can pull it out.
Line the base of the tin with graham crackers in one even layer.
Whip the cream to soft peaks, then add the condensed milk and continue to whip until thoroughly mixed. Spread 1/3 of the cream over the graham crackers, followed by 1/3 of the mangoes. Repeat the cracker/cream/mango process twice more, finishing with a layer of mango at the top.
Leave to chill in the freezer for a minimum of 4 hours, overnight is best.
Once ready to serve, remove the tin from the freezer and using the greaseproof paper, pull out the pudding. Slice and serve.