Soak mutton liver in vinegar for 30 minutes. Give it one rise before cooking.
Heat mustard oil and fry the potato pieces to a golden colour. Take them out and set them aside.
In the same oil (you can add more if you want) add bay leaf, 1-2 green chillies, then cardamom, cinnamon and cloves.
As it starts to release aroma, add the onions and start frying them.
Once the onions have softened, add garlic paste and ginger paste.
Keep frying this till the raw smell goes (you can sprinkle water if it’s sticking to the bottom).
Now add the chopped tomatoes and red chilli powder, turmeric powder, cumin powder and coriander powder.
Sprinkle water and let the spices cook with the tomatoes. When you see oil releasing from the sides, add the potatoes and mix them up.
Since the potatoes are almost cooked, you can add the mutton liver now and fry along with the spices and the potatoes (basically koshano).
You can intermittently, add warm water and cover and let the liver cook. It takes about 10- 15 minutes.
You can take one pc out, cut it to check if it’s cooked.
Then add a pinch of Bengali garam masala, ½ tsp of sugar, adjust the salt and add more green chillies.
Mix this up till it reaches the right consistency and then garnish with fresh coriander leaves
Serve with rice or roti