Peel the mangoes and grate sour mango finely. Take half of the sesame oil and add mustard seeds.When it splatters, add 1/2 tsp fenugreek seed powder and 1/2 tsp asafoetida. Add grated mango, add salt and fry well till the moisture is gone and it becomes a non-sticky paste. In the end add the red chilli powder and stir well for 2 min. When it cools transfer it to a bottle and store in refrigerator