Cook the potatoes in boiling salted water until tender. Add the peas and cook for a further 30 seconds. Drain and set aside. Tip the cumin, coriander and cardamon into a frying pan and toast over a medium heat for 1 minute. Coarsely grind the onion seeds using a pestle and mortar.
Heat the oil in a large frying pan, add the onion and cook until soft. Add the garlic, ginger and chilli and cook for 30 seconds then add the spices. Continue to cook for 1 minute, then add the diced potatoes and peas. Mix well and cook for 3–4 minutes, stirring frequently. Remove from the heat, add the chutney and chopped coriander and season well.
Preheat the oven to 190°C/375°F/gas mark 5. Lay a sheet of filo pastry on the work surface and brush with melted butter. Lay another pastry sheet on top and cut into strips 7 cm wide then brush with the melted butter. Put a spoonful of the potato mixture onto the top left hand corner of each strip. Fold over to make a triangle and continue folding down the length of the strip to completely encase the filling. Repeat with the remaining filling and pastry. Arrange on baking trays and bake for 25 minutes until golden and crisp. Serve with pickles and relishes.