Marinate the Chicken: In a medium bowl, combine the chicken thigh chunks with all the marinade ingredients: plain yoghurt, 1 tbsp grated ginger, 3 crushed garlic cloves, 1 tsp turmeric, salt, and pepper. Mix well to coat every piece. Cover and set aside for at least 15 minutes (or up to 4 hours in the fridge).

Sauté the Onions: Heat the oil or ghee in a large, heavy-based frying pan or casserole dish over a medium heat. Add the finely chopped onions and cook gently for 10-12 minutes, stirring occasionally, until they are soft, sweet, and turning a lovely golden brown. This is a crucial step for the sauce's depth.

Add the Aromatics: Add the remaining ginger, garlic, and the optional green chilli to the pan. Cook for another 2 minutes, stirring constantly, until fragrant. Be careful not to let the garlic burn.

Bloom the Spices: Turn the heat down to low. Add the ground cumin, ground coriander, remaining turmeric, and chilli powder to the pan. Stir continuously for about 60 seconds. You'll notice the spices become incredibly fragrant; this is the flavour base of your homemade curry. You can learn more about the science behind blooming spices in this excellent guide.

Create the Sauce Base: Pour in the tin of chopped tomatoes. Use the juice to scrape up any delicious browned bits from the bottom of the pan. Increase the heat to medium, bring to a gentle simmer, and cook for 5-7 minutes, allowing the sauce to thicken and the flavour to concentrate.

Cook the Chicken: Add the marinated chicken and any remaining marinade to the pan. Stir everything together until the chicken is well-coated in the tomato and spice mixture.

Simmer to Perfection: Cover the pan with a lid, reduce the heat to low, and let it simmer gently for 15-20 minutes, or until the chicken is cooked through and tender. What works best for me is checking a piece of chicken after 15 minutes to ensure it's not overcooked.

Finish the Curry: Remove the lid and stir in the coconut milk and the garam masala. A spice blend like garam masala is traditionally added at the end of cooking to preserve its delicate aromatics. Let it bubble gently for a final 2-3 minutes without the lid to combine. Check the seasoning and add more salt if needed. Serve hot, garnished with fresh coriander.