Any true-blue Bengali will get all passionate upon hearing two words Kosha and Mangsho, and if they are in the same sentence following one another, then you have a slave for life Bengali.
Bengalis like the rest of the world are going so fast these days, they forget to slow down. Kosha Mangsho is like bhalobasha (love), you can’t just hurry either! “Kosha” is the process of slow cooking, frying to be precise. When it comes to kosha, you can actually taste time. Its about slow cooking meat that will just melt in the mouth. If this form of cooking appeals to you, keep reading the rest of this post.
Many Bengalis will agree with me when I say using the “kosha” technique is a living, breathing tradition in Bengali homes. It is traditionally cooked in a handi over slow fire for about an hour. 
They say it takes a lifetime to master a Kosha Mangsho. I am lucky to have come close to discovering the secret of a good Kosha Mangsho recipe by my mid-life. I took the same recipe and gave it a new attitude with Chaanp (Hindi/Bengali for rack of lamb or ribs).
Ingredients for Kosha Chaanp are:
500 grams rack of lamb or goat (Frenched)
1 medium size red onion chopped fine
Half cup plain yogurt
1 tablespoon ginger paste
1 tablespoon garlic paste
2 teaspoons green chili paste
1 teaspoon turmeric powder
1 teaspoon red chili powder
1 teaspoon coriander powder
Half teaspoon garam masala powder
2-3 tablespoons mustard oil
Couple of bay leaves
Pinch of sugar
Salt
And the last ingredient is TIME!
Start by marinating the ribs with yogurt, ginger-garlic-green chili paste and the garam masala powder. I let it sit in the fridge overnight.
One mistake I made was that I did not ask my butcher to cut the ribs for me. I did it myself with some help from the kitchen scissor. And I did it after marinating so that the meat softened a bit.
Start by heating mustard oil, when it smokes a little add the pinch of sugar and then the onions. The heated oil will caramelize the sugar and the onions will naturally get the rich color we want for our Kosha Chaanp. Add the bay leaf to punch up some flavor to the onions.
Fry the onions till they are almost brown. 
Add ribs without the marinade. Save it for later!
Brown the meat on all sides and add the dry spice powders- turmeric, red chili, and coriander. Mix well and keep frying. Scrape any spices and marinade that stick to your pan/pressure cooker.
Add salt to taste. The salt starts to do its job and will get the liquid out of the meat and marinade.
Keep cooking the meat. Just when you have enough color to the meat, add the marinade mixed with a little water. At this time, lower the heat to the lowest mark as the yogurt in the marinade could curdle on high heat. Cover and cook till the meat is done.
The last step is to crank up the heat and dry up all the extra liquid and moisture. Babysit the Kosha Chaanp as we don’t want any burned meat on our plates.
All the spices will cling to the meat and give it a nice thick texture. Serve hot with rotis or parathas.
P.S. You can follow the same recipe and cook shoulder pieces of lamb or goat and call it Kosha Mangsho! Voilà.
