heat the oil in a heavy bottomed pan or karahi.
Once the oil is hot add the onion and peppers. Fry until they are just blistering and colouring. remove the peppers and onions from the pan with a slotted spoon and put in a bowl.
turn the heat down on the pan and add the garlic and ginger. Fry for a few seconds
Add the Kashmiri chilli and stir through. Add the curry masala, tandoori masala and other spices. mix in and fry for 20 seconds or so. If they start to catch add a splash of the water/tomato puree.
Turn the heat up to medium and add the Tomato paste and water. let this simmer and reduce down almost to a paste.
now add a couple ladles of base sauce, stir in a and let reduce. Now add 3 ladles of base sauce and let reduce. Now you can add most of the base gravy (leave around 200ml for adjusting your finished sauce) and simmer until you have a thick sauce and see little craters appearing. Don't stir to often as the sauce reduces. You want the sauce to caramelise around the edges of the pan and then the caramelised edges can be stirred in to the sauce. That's where all the flavour is.
Now you can add your chicken, Kasoori Methi, garam masala, tomatoes, chillies, peppers and onions. Heat through for around 15 minutes, if the sauce is too thick add more base sauce 'till you have your preferred consistency and then add your chopped coriander. Heat gently for another 5 minutes. Taste and add extra salt to taste.
Serve your curry with some pilau rice and Indian bread such as naans or chapatis.