Preheat oven to 200C/400F/Gas 6.
Cut a diamond shape from the pastry and lay onto an oiled baking sheet.
Use a sharp knife to score a smaller diamond 1cm/½in inside the edge of the pastry, making sure that the cut is not made all the way through the pastry.
Brush the pastry with the beaten egg and place into the oven to bake for 10 minutes, or until the pastry is risen and golden. Remove from the oven and allow to cool.
For the mango mousse, place the mango into a food processor and blend until smooth. Spoon a small amount of this mango purée around the edge of a plate.
In a bowl, fold the remaining mango purée into the whipped double cream.
Add the vanilla seeds, icing sugar and chopped fresh mint and fold into the cream mixture to combine.
Using a sharp knife, carefully slice off the bottom of the pastry case and use a little of the mousse to secure it to the centre of a serving plate.
Spoon a generous amount of the mango mousse on top of the pastry base, then place the pastry lid on top.
To serve, dust with icing sugar and garnish with a fresh mint sprig.
