Cook rice according to the instructions on the packet. Clean, chop and cut the onions, cloves of garlic, ginger and mushrooms as required. Mix the cumin, curry, coriander powder and bell pepper in a bowl.
Fry the onions in a wok or in a large non-stick pan over medium heat in a little ghee or oil until translucent. Add the garlic and ginger and fry for 2 minutes. Add the spice mixture and fry for 30 seconds. Add the mushrooms and half of the broth, increase the heat and reduce until the liquid has almost boiled away. Add the remaining broth, 50g sour cream, sugar, butter and tomato sauce and bring to the boil. Mix in the rice, bring to the boil and then cover and let simmer for 20 minutes on a low heat (stir occasionally so that the rice does not burn).
Chop the coriander. Stir in the garam masala and 2/3 of the coriander. Serve decorated with the rest of the coriander.