Remove the stems of the chilli. Wash them and pat dry them completely. Let them dry overnight preferably.
Either using gloves or applying some oil in your hands, gently slit the chilli only from the centre. Repeat this process for all the chillies.
Using the back of a spoon, gently deseed all the chillies and remove the membrane too. Be careful not to completely slit open the chilli.
Discard all the seeds
Heat a pan or kadai and dry roast the mustard seeds (both black and yellow) on a low flame till they start popping. Transfer them to a clean and dry plate.
Next, dry the fenugreek seeds till slightly golden in colour. Transfer to same plate.
Next, dry roast the fennel seeds and cumin or jeera till they start popping. Transfer to plate.
In the same kadai, heat the oil till smoking point and keep aside. Let the oil cool completely.
Cool all the dry roasted spices.
Now just pulse grind the spices in a mixer grinder. Make sure to keep the spices coarse and do not make a powder out of it.
Transfer the spice mix to plate and add the remaining dry ingredients - turmeric powder, salt, asafoetida, amchur powder, kala namak, nigella seeds, carom seeds and mix well.
Now add the vinegar and around 2 tablespoons of the cooled oil to this mixture and mix well.
Now the stuffing mix is ready and can be filled into the red chillies.
Using a small spoon, carefully stuff this masala in each chilli. Make sure that there is enough stuffing. Repeat the process for all the chillies.
Now dip each of the chilli in oil and stack them in a clean and sterilized container.
Pour the remaining oil over the jar. If there is any leftover masala, you could mix this too.
This pickle is to be kept under direct sunlight for 3-4 days. Tie a clean muslin cloth around the mouth of the jar and keep the pickle under sun during the day time and bring it back indoors in evening. Repeat process for 3 to 4 days till the chillies become soft.
Once ready the chillies would be soft, the pickle can be kept in refrigerator for up to a year.