To start, prepare the samosa masala by lightly toasting cumin seeds, coriander seeds, and fennel seeds in a sauce pan on a low heat; do not use any oil and only toast them lightly, until their aroma is released.
Move the toasted seeds to a mortar and, using the pestle, crush them to form a coarse powder; set it aside.
Warm up some oil in the sauce pan and, once warm, add the samosa masala to it; allow the masala to gently fry on a low-medium heat.
Once the masala releases its aroma and it turns lightly brown, add the freshly chopped ginger and green chillies. Mix these well and allow them to fry until the smell of rawness has gone.
Next, add the red chilli powder, hing, turmeric powder, coriander powder and chaat masala to the pan and mix well; allow the spices to cook, which should take around one minute.
Add the boiled potatoes to the masala; ensure the potatoes are peeled and diced and they must not be overboiled. It is better to use cold potatoes at this stage, as they do not release much water.
Mix well the potatoes with the masala, then top the spiced potatoes filling with the lime juice and coriander.
Mix well and set aside to cool down.