In a dry skillet pan, add 2 tbsp coriander, 2 tbsp white cumin and 1 tbsp peppercorns. Turn the heat to medium and dry toast until the spices become fragrant.
Pour the whole, toasted spices in a spice grinder or mortar and pestle and grind the spices to a powder. Pour the spices into a small bowl, then add the ½ tsp red chili flakes and mix to combine. Set aside. This is your karahi masala.
In a Karahi (iron wok), cast iron skillet, or normal wok, add 1 cup of vegetable oil. Turn the heat to medium-high and warm the oil. Then add the crushed 10 cloves of garlic into the oil and saute for 3-5 minutes until fragrant.
Then add the chicken pieces and ½ tbsp of salt into the oil. Keep stirring and fry for 5-7 minutes until the outsides begin to brown. Then remove the chicken from the oil and set aside. Drain the oil from the wok but leave the garlic in the bottom.
In another pot, add ½ cup of vegetable oil and warm it. Add the 5 slitted green chilis into the vegetable oil along with the 2 lb whole tomatoes.
Put a lid on the pot and cook, stirring from time to time, until the tomatoes soften and the skins start to crack.
Remove the skin of the tomatoes with tongs, then crush the vegetables with a wooden spoon or spatula until the tomatoes are soft. Keep cooking on low heat until the sauce thickens a bit. Set aside.
Put the wok back on the heat and add the remaining ½ cup of vegetable oil. Heat until warmed. Then add the chicken pieces and tomato sauce into the wok. Mix well.
Add 3 tbsp of the karahi masala into the wok and mix to combine. Cook for 2 minutes on low heat.
Dissolve ½ tsp chicken powder in 1 tbsp of water and add into the wok. Mix and cook for a few more minutes.
Continue cooking the karahi, stirring occasionally, for another 20 or so minutes until the sauce reduces in half and the chicken is covered in a thick and flavorful sauce.
Garnish with 3 chopped green chilies, 2 tbsp green coriander leaves, and 2 inches ginger julienne. Serve with fresh tandoori naan.