Marinate chicken with red chilli powder, garlic paste, ginger paste, lemon juice and salt. Mix well and set aside for an hour. Dry roast half the peppercorns, half the cloves, 1 inch cinnamon, 1 bay leaf and almonds till fragrant. Cool and grind into a fine powder.
Add the ground powder to yogurt alongwith cardamom powder, cumin powder and ½ teaspoon turmeric powder. Mix well. Add yogurt mixture to chicken and mix well. Set aside for another hour.
Place tomatoes, onions, garlic cloves, cashew nuts, kasuri methi, honey, 1 inch ginger, 1 teaspoon Kashmiri red chilli powder, ½ teaspoon turmeric powder, salt, coriander powder, 100 grams butter in a pressure cooker.
Take a piece of muslin cloth and place on a worktop. Place remaining bay leaf, remaining cloves, remaining peppercorns and remaining cinnamon on it and seal to make a bundle (potli).
Add potli, 200 ml milk and 100 ml water in the cooker. Cover and pressure cook for 25-30 minutes. After 1 whistle, reduce heat and cook further. Remove from heat and rest for ½ an hour.
Discard potli and puree the cooked ingredients into a smooth gravy. Transfer into a deep non-stick pan.
Heat 1 tablespoon oil in another non-stick pan. Add marinated chicken and cook turning sides for 2-3 minutes or till lightly browned.
Add the chicken to the gravy, place the pan on heat and mix well.Add remaining milk, stir to mix and bring to a boil. Cover and simmer for 10-12 minutes. Switch off heat.
Heat coal piece on direct heat for 10-12 minutes.
Heat 1 tablespoon butter and remaining oil in another non-stick pan. Add chopped garlic and sauté till lightly browned.Add remaining Kashmiri red chilli powder, mix well and cook for ½ a minute.
Add some cooked gravy in the pan and mix well. Transfer this back to the rest of the gravy, mix well and cook for another 5-10 minutes.
Place a steel bowl in the pan with the chicken gravy. Put the heated coal piece in the bowl and add 1 tablespoon butter on it. Cover immediately and set aside for 5 minutes or till the smoky flavour gets infused into the gravy. Remove the cover and strain the coal butter into the gravy. Mix well.