Samosa Pie Recipe

a bit of oil, for cooking
1 onion, chopped
500 grams/17.6 ounces lamb mince (or beef if you prefer)
1 medium sweet potato (about 300 grams/10.5 ounces), peeled & grated
2 garlic cloves, chopped or minced
a piece of fresh ginger the size of the width of your thumb, peeled & grated or finely chopped
2 tablespoons curry powder (I used a medium-strength powder)
1 tablespoon tomato paste
1 tablespoon flour
300 ml/10 fl. ounces stock (I used beef)
about 100 grams/3.5 ounces frozen peas
a good handful fresh coriander, chopped
juice of ½ a lemon
salt & pepper
3 to 4 sheets filo pastry
1 teaspoon cumin seeds