Prepare the Base: Heat the oil in a large, heavy-bottomed pan or Dutch oven over a medium heat. Add the chopped onion and cook gently for 8-10 minutes, stirring occasionally, until it's soft, sweet, and translucent.

Add Aromatics: Add the minced garlic and grated ginger to the pan. Cook for another minute, stirring continuously, until fragrant. Be careful not to let them burn.

Toast the Spices: Stir in the turmeric, cumin, ground coriander, and chilli powder. Cook for one full minute, stirring constantly. The spices will become incredibly aromatic. What works best for me is to keep the heat on medium-low during this step to prevent the spices from catching and turning bitter.

Sear the Chicken: Add the chicken pieces to the pan. Turn up the heat slightly and cook for 5-7 minutes, stirring, until the chicken is sealed and lightly browned on all sides.

Create the Sauce: Pour in the chopped tomatoes and the can of coconut milk. Add the sugar, and a generous pinch of salt and black pepper. Stir everything together well, scraping up any browned bits from the bottom of the pan.

Simmer Gently: Bring the curry to a gentle simmer, then reduce the heat to low, cover the pan with a lid, and let it cook for 15-20 minutes. The sauce should have thickened slightly, and the chicken should be cooked through and tender.

Finish and Serve: Remove the pan from the heat. Stir in the garam masala and most of the chopped fresh coriander (save a little for garnish). Let the curry stand for 5 minutes for the flavours to meld, then taste and adjust the seasoning if necessary. Serve hot, garnished with the remaining coriander.