In a bowl, whisk egg yolk and sugar together until light and frothy.
Heat milk until scalding in a heavy-based saucepan, then pour it slowly into egg mixture, whisking constantly.
Strain milk and egg mixture back into pan and place it over heat, stirring all the time, until it thickens. Let cool.
Mash mango flesh with a fork for chunky texture, or put it in an electric blender and whiz to a puree.
Strain cooled custard into a bowl and whisk in whipping cream.
Beat mango puree until thoroughly mixed, then pour into an ice cream maker. Churn until frozen.
Without an Ice Cream Maker - Alternatively, pour mixture into a freezer-proof container and freeze for 2-3 hours, beating with a fork periodically (Continue to check the mixture every 30 minutes) and stirring while it freezes to break to ice crystals.