Put the custard powder into a bowl and blend it into a smooth paste with a little of the milk.
Add the rest of the milk and stir over gentle heat till it thickens and comes to a boil.
Add the sugar, stir to dissolve and let it cool.
Stir in the mango pulp.
Separately, dissolve the gelatine in the water over gentle heat.
Add to the mango mixture and stir well.
Add the thin cream, stir and pour into the mould.
Leave to set in the refrigerator.
Before serving, unmould, and fill the centre with the whipped cream.