Remove the mangoes from the brine and cut them each in half (including the soft seed) and grind them with the green chillies and coconut, adding just enough water, into a fine paste.
Add this paste and salt to the yogurt and mix well. Remember the mangoes have been preserved in brine and add the salt accordingly.
The coconut-yogurt paste should be the consistency of a thickish gravy and will resemble a coconut chutney. Taste-wise, it should be slightly spicy with a slight tang from the mangoes.
If you are not serving this immediately, you may refrigerate it.
Just before serving, heat the oil in a small pan and add the mustard seeds. When they splutter add the lentils and and stir a couple of times till they start becoming golden. Break the red chillies into 2 or 3 and add them to the oil. Now add the fenugreek seeds and the asafetida powder and stir a couple of times. Do not let the fenugreek seeds brown too much.
Take the oil and spices off the heat, add the curry leaves, mix once again, and pour this oil-spice mixture into the araitchukalakki.
Serve with warm rice, a vegetable side dish and pappads/ sun-dried fritters (appalam or karuvadam). Araitchukalakki is also served as a side dish along with this or this molagootal and rice.