Add the saffron strands to the bowl with the yogurt and let the saffron bloom in the yogurt for 10 minutes at least. We will use this to add color and aroma to the Rogan Josh.
Start with a large heavy bottom pot such as a dutch oven which is ideal for both searing meat and slow cooking on the stovetop.
Preheat the Dutch oven and add the mustard oil. Let that heat up and add sliced onions.
Cook the onions in the oil until they start to caramelize and turn brown in color. The caramelization gives the organ josh both a darker color and a strong flavor profile.
Add the whole spices - bay leaves, cinnamon, cardamom, cloves, and minced ginger, and garlic.
Add the meat pieces - for rogan josh, you can use either lamb or goat (mutton) meat. I have used lamb neck-pieces, but lamb shoulder also works very well.
Sear the meat on high heat to give a slight caramelization to the meat. Use your spatula to move the meat around so that it cooks evenly.
Add the spice powders - coriander, garam masala, turmeric and the key spice for rogan josh - Kashmiri chili powder. If the amount of chili powder seems high here, don't worry, Kashmiri chili powder is very mild, and is used mainly to give the curry a nice red color.
Add the tomatoes. Give it all a good mix, add 1/2 a cup of water and remove any residue sticking to the bottom of the pot. Cover with a lid and cook for 10 minutes.
Then, remove the lid, season with salt, and add the saffron-yogurt mixture. Give it a good mix and make sure there is no residue stuck to the bottom of the pot. Cover with a lid and let the curry simmer on medium heat on the stovetop for 1 hour 30 minutes. Check the tenderness of the meat - it should easily come apart when pierced with a fork. If not, cook for a further 10-15 minutes until tender.