Prepare your lamb or mutton pieces by rinsing with water, and patting dry with kitchen paper
In a large mixing bowl, add the lamb pieces, followed by freshly crushed ginger and garlic. Add yogurt, enough sea salt to season the meat and turmeric. Mix well and cover and keep aside for at least 1 hour or even overnight.
While the meat is marinating, heat a heavy-bottomed Dutch Oven or a heavy pot on the stovetop.
Add mustard oil and let the oil heat up.
Once the oil is hot, add sliced onions, and saute in mustard oil for 5-7 minutes until the onions and browned.
Once the onions are browned, add the marinated meat. Mix with the onions.
Add all the spice powders - garam masala, cumin, coriander, fennel, Kashmiri red chili powder. Mix again.
Add the concentrated tomato paste. Mix well.
Add 1/2 a cup of water and mix the meat well.
Cover the pot with a lid and let it cook on medium-low heat for 30 minutes.
After 30 minutes of slow-cooking, open the lid check to see if there is any residue sticking to the base of the pot.
Use the spatula to remove any residue at the base. It is IMPORTANT that you remove the residue at the base with your spatula before you let it cook again.
If you like your gravy to be thicker, add another 1/2 cup of water, then cover the pot with the lid again. Continue to cook covered, on low-medium heat for 45- 50 minutes, until the lamb is cooked and tender.
To check for doneness, use a fork - it should easily pierce the meat and the gravy should be thick.
Your lamb karahi or mutton karahi is ready to be served with tandoori roti or naan or basmati rice.