NB:This pastry is short and crumbly, it may break up when you are trying to roll it out. If this happens, try coarsely grating it directly into the tin and then quickly press it up the sides and into the shape of the tin. No one will know the difference!
Preheat the oven to 200°C, gas mark 6.
Place the butter, flour, salt and sugar into a food processor and blend for 20 seconds. Alternatively, you can rub together by hand.
Add the egg yolk and cream and blend again or mix until the dough just comes together. Do not overwork the dough or the pastry will be tough. Wrap the pastry in cling film and chill for 1 hour.
Grease a 20cm (8in) round, fluted, loose-bottomed flan tin, 3cm in depth.
Roll out the pastry on a lightly floured work surface and use it to line the prepared tin. Trim the edges and prick the base with a fork, then chill for about 20 minutes.
Line the pastry case with foil or non-stick baking paper and a thin layer of baking beans. Bake 'blind' for 15-20 minutes, then take the pastry case out of the oven and reduce the temperature to 180°C, gas mark 4.
Carefully remove the beans and the foil or paper from the case, then return it to the oven for 3-5 minutes until lightly golden.
Place the lime zest and juice in a saucepan with the vanilla seeds, sugar and coconut milk, then heat gently until the sugar dissolves.
Mix the cornflour in a small bowl with 4 tablespoons of cold water, then stir it into the coconut mixture. Pour into a saucepan. Bring to the boil and cook for 2-3 minutes until thickened, stirring constantly. Remove from the heat and then allow to cool slightly.
Finally, beat in the egg yolks and butter and return to the heat to cook gently for 6-8 minutes, stirring constantly, until thick enough to coat the back of a spoon. Pour the filling into the pastry case and allow to cool completely.
Once the filling is cool, preheat the oven to 180°C, gas mark 4.
Place the egg whites in a large bowl and whisk into soft peaks, then gradually whisk in the sugar a spoonful at a time to make a stiff, glossy meringue. Spoon the meringue on top of the filling, spreading it out evenly to make sure it forms a good seal with the pastry edge. Swirl the top of the meringue with the tip of a knife and bake the pie for 15 minutes or until it is lightly golden and crisp on top.
Allow the pie to cool slightly and then carefully remove the tart from the tin. Allow to cool completely before chilling for a few hours or overnight until completely set. To serve, cut into slices and arrange on plates and serve with whipped cream.