1. Wash Mutton pieces thoroughly and pat dry those.
2. Make a paste of two onions and finely chop the rest.
3. Now, marinate Mutton pieces with Grated Raw Papaya, 1 tsp each of Turmeric Powder, Cumin Powder, Coriander Powder, and Garam Masala Powder, 1 Tbsp. Mustard oil, a little salt, 1/2 Tsp. Sugar and also 1 Tsp. each of ginger and Garlic Paste and Onion paste.
4. Add half of the curd as well.
5. Mix everything and give the marinated mutton rest for around 6-8 hours.
6. Take rest of the Mustard oil in a deep bottom pan and heat the oil sufficiently.
7. Temper the oil with Bay leaves, Dry Red Chillies, and Hing and then add 1 Tbsp. of sugar and cook until the sugar dissolves and caramelized.
8. Now add chopped onion and cook until the onion turns brownish in color.
9. Add Ginger and garlic paste and cook for another 4-5 minute in medium flame until oil separates.
10. Now add curd and mix thoroughly.
11. Add rest of the Turmeric Powder, Cumin Powder, Coriander Powder, and chili powder and cook for one more minute.
12. Add salt as well
13. Now add marinated mutton pieces along with the marination to the spice mix and start cooking on medium flame.
14. Next step is known as “Koshano” in Bengali which means cooking on high flame without adding water and it requires frequent mixing.
15. Cook for at least 4-7 minutes on high flame and stir frequently.
16. Check the gravy for salt and other spices and if require adjust spices accordingly.
17. Cook on low flame for around 1 hour.
18. Stir in between.
19. No need to add water at this moment as Mutton will release moisture.
20. Cook till the mutton soften but remain in shape.
21. Now add chopped green chili.
22. Add 1 cup boiling water and cook until the gravy reaches desired consistency.
23. Add Ghee and Bengali Garam Masala Powder and cook for another 1-2 minutes and switch the flame off.
24. Kosha Mangsho is ready to serve.

Kosha Mangsho aka Mutton Kosha Recipe Video