Preheat your slow cooker to high.
Heat the butter and oil in a large pan, add in the onion and chicken and cook for 5-6 minutes until the onions are softened and the chicken is sealed.
Add in the garlic, ginger, salt, garam masala, curry powder, paprika and cinnamon. Stir and cook for 1-2 minutes. Add in the stock, tinned tomatoes, tomato puree, sugar and cardamom. Stir then pour into your slow cooker and cook for 4 hours on high or 6 hours on low.
Remove the cardamom then stir in the cream and allow to heat through.
Serve with rice, sprinkled with some coriander & some naan bread on the side.
You can freeze this. Instead of cream you can use coconut cream.