In a bowl take all the ingredients under the marinate head and the chicken pieces.The chicken pieces should be 1" inch in size. Mix well and keep aside for atleast 2 - 3 hrs
Blanch, peel and puree the tomatoes. Keep aside.
Soak the cashewnuts for 2 - 3 hrs in hot water and then strain and grind the cashewnuts into a fine paste

For the curry heat the pan and add butter and immediately add the garlic paste.
Now add the sliced green chilli. Also add cumin powder, red chilli powder and salt. Add 1 tblsp water and mix well.
Add the tomato puree and cook till the gravy leaves the side.
Lower the flame and add the cashewnut paste and stir constantly.
Now add the tomato ketchup, sugar and 1/4 cup water.

Meanwhile in a separate pan shallow fry the marinated chicken pieces for 4 - 5 minutes. If overcooked then the chicken will get hard and stiff. Keep aside.
Once the gravy comes to a boil add the chicken pieces. And cook for a minute.
Now lower the flame add the milk and stir well. Cook for another minute and then add the cream. Mix well

Now add the garam masala and crushed fenugreek leaves. Mix well.
Transfer the chicken to a serving bowl and garnish with chopped coriander leaves, crushed fenugreek leaves and swirls of cream.
Restaurant style Indian butter chicken is ready to be served with naan or tandoori roti. Authentic butter chicken is a very high calorie dish yet very very tasty. So dig in

Note:
1. Milk should be at room temperature before adding to the gravy.
2. Add milk and cream at low flame only.
3. Add the garam masala only at the end