Marinade chicken cubes for 30 minutes or overnight in a large bowl with Tandoori Masala Powder, Garlic Paste, Ginger Paste, Green Chilli Paste, Yoghurt, Lemon Juice, Garam Masala Powder, Kashmiri Chili Powder, Cumin Powder, Coriander Powder, Turmeric Powder, Kasuri Methi and Salt. Cover the bowl with cling film/plastic wrap before placing into the fridge.
Place marinated chicken in a single layer in an oven tray and grill for 10 minutes each side till golden brown and charred. Or place into an oven tray and bake at Gas Mark 4/200 C/390 F for 20 minutes, turning midway.TIP - The length of time depends on the thickness/size of the chicken chunks. I like to keep them at 1 1/2 - 2 inches. Melt Butter in a large pot over medium high heat. Once it begins to foam, add the Oil.
Add the Onions if using and cook over medium heat till golden brown. Around 10 minutes.
Stir in Ginger paste, Garlic paste and Green Chilli paste. Saute for 1 minute.
Pour in the Tomatoes. Then bring to a simmer. Lower the heat, cover the pot and cook for 8 - 10 minutes.NOTE - At this stage, the Butter/Oil will begin to seperate at the edges and the sauce will thicken. Stir in the ground spices - Cumin Powder, Garam Masala Powder, Coriander, Kashmiri Chili Powder, Turmeric Powder, Black Pepper powder and Salt. Simmer for 5 minutes.
Stir in Sugar.
Blend the sauce with a immersion blender to a smooth paste. If you feel like it is thick, add a couple of tablespoons of Milk or water and blend again. Transfer the Butter Sauce back into the pot and bring to a gentle simmer.
Add the cooked Chicken and excess marinade from the oven tray.
Sprinkle over Kasuri Mehthi.
Mix with a spoon and then simmer on medium low heat for 5 minutes before pouring in the Cream. Simmer for 2-3 more minutes.
Garnish the Butter Chicken with Coriander. Serve with Naan or Rice.