Spray the bottom of a large casserole dish about 8 times with the low calorie cooking spray. Heat the casserole dish on a hob, on high heat, until the cooking spray begins to bubble then turn the heat down to a medium heat.
Add the ginger and garlic paste then the diced onions and sauté the onions until soft for about 8 – 10 minutes. Add small amounts of hot water if the mixture begins to stick.
Stir in the chilli powder, garam masala, chopped tomatoes and the tomato puree and cook for about 10 minutes until soft. Add small amounts of hot water if the mixture begins to stick.
Stir in the salt and sugar. Turn off the heat and allow to cool a little.
Puree the mixture to a paste in a blender / food processor.
Add the paste back to the casserole dish, add the stock, cinnamon stick and bay leaves.
Turn the heat back on, bring to a boil and then turn down to simmer, with the lid on for 15 minutes.
Remove the cinnamon stick and the bay leaves.
Add the lamb, put the lid back on and cook for 1.5 hours, stirring the curry every 15 – 20 minutes or so. Top the curry up with hot water if necessary during this period.
Serve the curry garnished with chopped fresh coriander and some basmati wholegrain rice.