For the meringue, preheat the oven to 200C/400F/Gas 6.
Whisk the egg whites in a bowl until soft peaks form when the whisk is removed. Whisk in 100g/3½oz of the caster sugar, a little at a time, until well combined.
Continue to whisk until the egg whites are stiff and glossy.
Heat the milk, cream and vanilla seeds in a lidded saucepan until simmering.
Lightly oil 2 tablespoons with the vegetable oil and use them to shape quenelles of the meringue mixture. Carefully place them into the simmering milk.
Cover with a lid and poach for 4-5 minutes, or until just cooked through.
Remove the meringues form the milk mixture with a slotted spoon and set aside on kitchen paper.
Heat the remaining 100g/3½oz sugar in a frying pan until the sugar become pale golden-brown.
Place the base of the frying pan into a larger pan of cold water to stop the caramel cooking, then set aside to cool slightly.
Using a potato peeler, peel shavings of coconut flesh and place them onto a baking tray. Toast them in the oven for 3-4 minutes, or until pale golden-brown.
For the custard, strain the milk mixture used to cook the meringues into a clean saucepan, return to the heat and add the coconut liqueur.
Whisk the egg yolks and sugar in a bowl until well combined. Whisk in the milk mixture until well combined.
Return the mixture to the saucepan, add the chopped mango and cook over a low heat, stirring continuously, until the custard has thickened enough to coat the back of a spoon.
To serve, spoon the mango custard into serving bowls and place the meringue on top. Scatter over the toasted coconut. Use the back of a spoon to pull strands of the caramel mixture and drizzle over the top of the meringue.