Preheat the oven to 200C/400F/Gas 6.
For the mixed berry parcel, dust the pastry with icing sugar and spoon the berries into the centre.
Brush the edges of the pastry with the beaten egg and fold the corners up into the centre. Pinch the edges together to seal the filling inside the pastry.
Place the parcel onto a non-stick baking sheet, transfer to the oven and bake for 10-12 minutes, or until slightly risen and golden-brown.
For the coulis, place the icing sugar and berries into a food processor and blend until smooth. Strain the mixture through a sieve to remove the pips.
To serve, pour a pool of coulis onto a serving plate and top with the mixed berry parcel. Garnish with berries and fresh mint.