First make the pastry. Sift the flour into a mixing bowl then add the salt, oil and the carom seeds. Rub the oil into the flour with your hands so it is well combined then add 100 ml water. Bring the dough together and knead briefly until it forms a smooth and soft ball.
Cover the bowl with a cloth and leave to rest at room temperature for an hour.
Meanwhile make the filling. Bring a pan of water to the boil and add the potatoes. Cook until soft but still holding their shape.
Heat the oil in a frying pan and add the fennel and cumin seeds. Once they start sizzling add the peas and cook until done. Add the grated ginger, green chillies, ground coriander and cumin and cook for a minute.
Add the cooked potatoes to the pan , mix well and cook for 2-3 minutes to heat through and mingle the flavours.
Chop the coriander and add with the salt. Continue to cook over a low heat for 2-3 minutes. The vegetables should be well coated with the spices. Check the seasoning, then remove from the heat and leave to cool.
When you are ready to start cooking heat a frying pan on a very low heat. While it is heating divide the rested pastry into 5 equal sized balls. Roll each into a circle on a lightly floured work surface to approximately 15 cm in diameter.
Put the rolled pastry into the pan, warm on both sides then cut in half. Repeat with all the other roti.
Brush the edges with water. Fold the semi circle in half, bringing the straight edges together to make a cone, and fill with the filling. Pinch and seal the open edge then push it with a fork. Repeat until all the remaining dough is made into samosas.
Heat a deep heavy based pan, half fill it with oil and heat it to 180 C. Deep fry the samosas, two at a time, for 4-5 minutes until light brown and crisp. Remove with a slotted spoon and transfer to a plate lined with kitchen paper.
Fry the rest in batches and serve while still hot.