Cut the lemon into small bits keep aside also mix chili powder, coriander powder, asafoetida, fenugreek and salt adding 1/2 cup water and keep it ready.
Heat oil add mustard when it crackles add whole red chili pieces, curry leaves add lemon bits and green chili and fry until the lemon becomes brown and almost crisp remove and keep aside.
Then in the same pan pour the powders mixed in water and more water if needed (enough to cover the lemon) let it boil now add lemon fried and boil until it thickens.Add the jaggery piece switch off flame.Once it is cool keep it in an airtight bottle.It can be used immediately.
Serve it for sadhya or for kanji
Notes
Best achar to have when u have fever or when u don't feel any taste on ur tastebuds
If you do not get vadugapuli naranga use really large lemon with slightly thick peel like I have used here.
If the lemon is not tangy and sour enough some tamarind squeezed (or around 1 tsp paste)also should be added along with the spice powders in step 2.I did not use tamarind as pickle gets spoilt with in 2-3 days -according to Amma.