Wash the gooseberry and wipe it with a cloth or tissue paper. Soak the tamarind in half a cup of water.
Dry roast the mustard and methi seeds for a few minutes in low flame, till the mustard turns whitish and the methi starts browning.
Cool this down and powder it in a motor and pestle. Add the garlic pods to this powder and roughly crush them.
Grind the tamarind, the whole red chillies and the salt in a mixer to a smooth paste using the water in which the tamarind was soaked. In an earthenware pan, heat up 2 tbsp of sesame oil. Shallow fry the gooseberry in batches for a few minutes till it mildly browns up on the surface. Keep aside.
In the same oil add crushed mustard-methi-garlic mix and give it a good stir.
Add the ground paste, and the hing, turmeric powder, and jaggery.
When it comes to a boil add the fried gooseberries and curry leaves.
Taste test, balance the spices, and let it cook till oil separates. Add the lemon juice just before turning off the stove.
Cooldown and transfer to a glass or ceramic container preferably. Let it mature for at least a week before consuming, but I bet it's not going to last that long.