Marinate chicken in yogurt, lemon juice, salt and lemon juice for at least an hour.
In the meantime, chop up tomatoes, onions, chillies, garlic and ginger so they are easier to blend later.
Heat up oil in cooking pot. Add chopped vegetables and cashew nuts. Stir-fry over low to moderate heat for a few minutes, until the onions start to brown. Set vegetables aside until cool enough to handle.
Transfer vegetables to a blender. Blitz until you achieve a smooth pourable paste.
Heat up oil in frying pan. Fry marinated chicken pieces a few minutes on both sides until you achieve browning. At this stage, the chicken is not fully cooked inside. The cooking will be completed in the sauce later.
Now, heat up butter in cooking pot. Add a stick of cinnamon, coriander and cumin powder.
Add sauce in. Cook for 10-15 minutes to extract maximum flavour. Remove cinnamon stick.
Mix in chicken and let simmer for 10-15 minutes.
Season with sugar, salt and garam masala. Add a dash of cream, as per your liking. Serve!