1. Heat the oil in a large pan and cook the onion and carrot for 4–5 minutes until softened. Stir in the lamb, curry paste and stock and simmer for 15 minutes until the liquid evaporates.
2. Tip the lamb mixture into a large bowl and stir in the frozen peas and cold cooked rice straight from the pack.
3. Preheat the oven to 220ºC, gas mark 7. Cut the pastry into quarters then roll out each piece to make an 18cm square. Divide the filling between the squares. Dampen the edges with milk then pull the four corners up so they meet in the centre. Firmly press the edges together to seal. Repeat to make four pasties.
4. Transfer the pasties to a large, non-stick baking sheet and brush with milk. Sprinkle over the nigella seeds and bake for 20 minutes until puffed and golden brown.