Wash lemons thoroughly and wipe with a clean towel to remove all moisture. Heat half of gingelly oil and saute lemons in the hot oil, until the skin become tender. Prick the lemon fruits in several places all around and place them in a bowl.
Make a paste of ginger, garlic and green chilly.
In a pan, add 3 tsp of gingelly oil. Splutter mustard seeds and fenugreek.
When it sputters completely, add ground ginger, garlic and green chilly paste and curry leaves into it and saute well until its raw smell disappear.
Lower the flame and add red chilly powder and turmeric powder followed by asafoetida powder and saute for a few seconds.
Heat vinegar separately in a pan and let it cool for some time and add it to the prepared masala. Add required salt and sugar. Taste, and add extra salt /vinegar if needed.
Add the lemon into the prepared masala, and mix well. If the gravy seems thick, add some boiled water.
Transfer the whole lemon pickle into a mud jar locally known as bharani or a ceramic jar. Clean the jar with hot water, and make sure the jar and lid is completely dry before you use it for storing.
Heat 2 tbsp of gingelly oil, and allow it to cool and then pour the oil on top of the pickle. This will prevent fungus growth, and give an authentic taste.
Start using the lemon pickle (naranga achar) once it settles, after a few days.