Wash ker and soak it in buttermilk for 3 days at room temperature. This helps to remove the bitterness of ker. You can also use beaten curd mixed with 1 cup of water and 2 teaspoons of salt instead of buttermilk.

Soak sangri separately in water overnight starting on the 2nd night.

To process the ker, drain the buttermilk or curd mixture and wash the ker 5-6 times with water.

Then add ker to boiling water and boil for 2 minutes. Then cover with a lid and let it blanch for 5 minutes.

Drain the water from sangri as well, and boil it separately in new water for 2 minutes. Again leave it covered with a lid for 5 minutes.

Drain the water from both ker & sangri. Spread them out on a clean cloth or paper and let them dry completely.

Heat 3 tablespoons mustard oil in a pan and fry the ker & sangri in it.

Let the mixture cool down completely.

Now grind the whole spices i.e. rai (black mustard seeds), dana methi (whole fenugreek seeds), split yellow mustard (sarson ke beej), saunf (fennel seeds) and kalonji (nigella seeds). Add these to the ker & sangri.

Also add amchur (dry mango powder), haldi (turmeric powder), red chilli powder, salt and heeng (asafoetida) to the mixture.

Mix everything well and transfer the mixture to a jar.

Add the remaining mustard oil to the jar. Make sure not to overfill, and leave some space at the top.

Store the pickle at room temperature. Stir with a spoon 2-3 times a day.

Ker Sangri achar will be ready in 8-10 days. Store it at room temperature and serve it along with any Indian meal.