Steam cook the de-seeded Indian gooseberry wedges in a pressure cooker without adding any water. It's enough to cook up to 3 whistles in medium flame.
When the gooseberry pieces cool down to room temperature put them in to mixer jar. Also add other spices like red chillies, cumin seeds, blackpepper, turmeric powder, salt, asafoetida and jaggery.
Grind them all together in to fine puree. Next heat a pan with oil, mustard seeds and curry leaves. As the seeds sizzle pour the ground puree from above step and saute for few minutes till it thickens.
Notes
You can steam cook the gooseberries first for ease of separating the wedges from it's seed.
I have used Kashmiri red chillies which are less in spice. If you are using spicy variety red chillies, then reduce the quantity.
You have to balance the tartness of gooseberry with appropriate spice and jaggery to enjoy perfect tasting thokku.
Above mentioned quantity of jaggery and chillies led my thokku towards perfect taste, so adjust them as per the tangy-ness of gooseberry that you have.