For the sweet potato pie, cook the sweet potato in boiling water for 6-7 minutes, or until tender. Drain, then mash with the vanilla seeds and brown sugar until smooth and creamy.
Spoon some of the sweet potato mixture into a 10cm/4in chefs' ring until the ring is two-thirds full.
In a large bowl, whisk the egg whites until soft peaks form when the whisk is removed from the bowl, then gradually whisk in the caster sugar until stiff and glossy. Spoon the meringue into a piping bag and pipe over the top of the sweet potato mash. Using a mini blow torch, brown the top of the meringue until golden-brown.
For the pine nut brittle, tip the sugar into a small dry frying pan and when it starts to melt, add the pine nuts and stir frequently until the nuts are toasted and the sugar is caramelised and a nutty brown colour. Pour onto silicone paper to cool.
To serve, carefully remove the chefs' ring. Break up the cooled pine nut brittle and scatter around the edges of the plate.
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