For the oxtail: Rub the spices into the oxtail and fry them until nicely coloured on all sides. Add the meat to the pressure cooker and cover with water. Cook under pressure for 50 minutes until tender and falling off the bone. If you don't have a pressure cooker, cover with water in a normal pot, bring to the boil and simmer gently for approx 2-3 hours until done. Once cooked, drain the water (but keep it) and pick the meat off the bones. Keep the meat and liquid aside (separately)
For the lentils: If using a pressure cooker, cover the lentils with water and pressure cook for 30-35 minutes. If you don't have a pressure cooker, make sure the lentils have been soaked overnight before cooking in a pot (drain the lentils and cover with 2 litres water, bring to the boil and simmer for 1 hour)
In another pan, heat the veg oil and fry the cardamoms and bay leaf, followed by the onions, salt and chopped garlic. Fry them on medium heat until golden.
Drain the chopped tomatoes and keep the liquid. Add the pulp to the onions along with ginger-garlic paste and chilli powder. Fry on medium heat for another 10-15 minutes till caramelised and dark in colour. Once the lentils are cooked, drain them and add them to the onion-tomato mix. Fold in the picked oxtail and the oxtail liquor (if you're vegetarian, just use the water from the lentils), followed by the butter, cream, garam masala and crushed fenugreek leaves. Check for seasoning.
Fill the smoking gun chamber with some wood chips and direct the nozzle into the pot of lentils and place a tight fitting lid on top. Fire up the wood chips and fill the pot with the wood smoke and cover with the lid for 15 minutes.
Serve the lentils with some hot buttered naan or plain rice.