For the meringues, pour the milk into a wide saucepan, add the vanilla pod and warm over a medium heat until boiling, then reduce the heat to simmer.
Meanwhile, whisk the egg whites in a clean bowl, until stiff peaks form when you remove the whisk. Gradually add the sugar, bit by bit and continue whisking until the eggs become glossy and stiff.
Make three quenelles or oval shapes out of the meringue mixture and place them into the milk. Poach for a minute on each side or until cooked through.
For the brittle, melt the sugar in small frying pan over a medium to high heat, without stirring, until golden brown. Carefully add the cashew nuts and gently shake to mix them with the melted sugar. Pour over greaseproof paper and leave to cool and set.
Once the brittle is cool and set, break into pieces.
For the purée, place the sweet potato and icing sugar into a bowl and mash together well. Season, to taste, with a pinch of salt.
To serve, spoon the sweet potato mash onto two plates and top with the meringues. Garnish with the cashew nut brittle.
