Heat one tablespoon of the oil in a heavy-based frying pan. Fry the mustard seeds, curry leaves, ground turmeric and ginger, stirring often, for one to two minutes, until fragrant.
Add the crab meat, salt, chillies, lime zest and coriander mixing well, and cook for a further two to three minutes.
Mix together the water and flour to make a flour paste.
Fold a pastry sheet over to make a strip. Place a portion of the crab mixture in one corner of the pastry strip and fold the pastry over into a triangle. Fold the triangle along the strip, sealing the edges with the flour paste.
Repeat the process making 24 samosas in total.
Heat the oil for deep-frying in a deep fat-fryer or wok until hot. To test if the oil is hot enough, drop a small piece of bread into the oil - if it sizzles immediately and starts to change colour after a few seconds, it's ready. Fry the samosas in batches until golden-brown, remove with a slotted spoon and drain on kitchen paper.
For more information on the spices used in Reza's recipes, look inside our Indian spice box.