Allow the pastry to come to room temperature before unrolling.
Meanwhile mix your sausage meat with the curry powder, mango chutney, breadcrumbs and a pinch of salt and pepper. Beat the egg in a separate bowl.
Place your pizza stone onto the cold BBQ and put the lid on. Turn the barbecue on and allow to pre-heat over a medium heat for 5 minutes.
Roll out the pastry, and slice into three strips. Cut these into three so you end up with nine equal squares. Brush the edges of each with the beaten egg.
Divide the mixture equally between the centre of each square and roll up, pressing the pastry edges together to seal. Crimp each edge together. Brush with the beaten egg and sprinkle with the nigella seeds.
Place the pasties onto the pizza stone and replace the lid. Cook on a low heat for around 20 minutes. Turn after 15 minutes. Try and avoid turning or moving before this time as the pastry may stick and tear.
Once the pastry is golden brown turn the BBQ off and allow the pasties to cool slightly before serving!