Wash and dry gooseberry with a clean towel and set aside.
Make tamarind pulp. Soak tamarind in 2 cups hot water for 15 minutes. Take the mixture in a blender and puree till smooth. Pass the ground tamarind puree through a sieve and extract the tamarind pulp. Now take the tamarind pulp in a pan and cook that for 10 minutes stirring constantly to evaporate the water content. Once the mix gets thick, take it in a clean glass bowl. Set aside and Allow this mixture to cool completely.
Make the Fenugreek mustard powder. Take fenugreek seeds and mustard seeds in a dry pan and roast till toasted. Take this mixture in a blender and powder to a fine texture. Set aside.
In a large kadai, heat sesame oil.Add in the gooseberry one by one carefully. Gently mix this using a spoon. Cover this with a lid and cook till gooseberry is cooked and gets golden brown. Once the amla is golden brown, remove them to a plate. Use a spoon or potato masher to slightly press over the gooseberry to crack them open so the pickle masala can enter the amla. Set aside to cool.
In the same gooseberry fried oil. Add in garlic cloves and fry till golden brown. Once the garlic is fried, add in mustard, fenugreek seeds, dry red chillies, curry leaves, asafoetida and mix well. Take it off the heat and allow it to cool for 5 minutes. Now add in turmeric powder and mix well. You have to allow the oil to cool completely.
Now in a mixing bowl, take cooled tamarind pulp, chilli powder, salt, powdered fenugreek mustard mixture and mix well. Pour the cooled tempered oil and fried gooseberry into the masala. Toss well to coat.
Transfer to a clean sterilised glass jar, set aside for 2 days and enjoy after 2 days.