Place the butter and water in a medium-sized saucepan and heat gently, stirring occasionally, until the butter melts, then allow the mixture to come to a rolling boil.
Meanwhile, sift the flour, spices and salt into a large bowl. Make a well in the middle and add the egg.
Pour the hot liquid into the flour and stir with a wooden spoon to mix.
Spread the mixture out on a large plate with the wooden spoon and allow to cool (about 15 minutes), then wrap in cling film and place in the fridge for 30 minutes until firm.
Preheat the oven to 220ºC (425°F), Gas mark 7. Make the pastry.
While the pastry is chilling, make the filling. Heat the olive oil in a saucepan set over a medium heat, add the onions, garlic and ginger, season with salt and pepper and cook until the onions are soft and slightly golden.
Grind the seeds in a mortar with a pestle, then add to the pan with the beef, tomato purée, mustard and Worcestershire sauce. Cook over a medium heat for 15 minutes or until the beef is cooked. Add the peas for the last 1–2 minutes of cooking. Add the chopped mint, then season to taste and allow to cool.
Roll the dough out on a lightly floured work surface until it is approximately 2mm (1/16 in) thick. Using a small saucer or something similar, cut the dough into 12cm (4 ½ in) circles.
Lay 1 generous tablespoon of the mixture on one half of the circle and brush the edge of the other half with beaten egg, then fold it over to form a semi-circle. Pinch the edges together to seal, making sure there is no air trapped inside, and mark the edges with a fork. Repeat until all the circles and filling are used up.
Brush the tops with beaten egg and bake in the oven for 15–20 minutes or until golden and a skewer inserted in the middle of each comes out hot. Serve hot or at room temperature.