Cut the chicken into quarters and pop in a bowl.
In a blender, add in roughly chopped ginger, garlic, green chillies and a dash of neutral oil. Blitz together into spreadable paste consistency.
Use half the paste for a marinade and massage into the chicken pieces and place to the side. Save the other half for later.
In a dry pan, add the cumin seeds, fennel seeds, cardamom pods and black peppercorns and toast over low heat until fragrant.
Add to a mortar and pestle and pound into a powder. Pop spice blend.
In a large pot over medium heat, add the coconut oil and allow to melt if needed. Add in the black mustard seeds.
When they begin to pop, cook for another minute before adding in the onion and the reserved paste from the chicken marinade.
Mix through and allow to soften for 5 minutes.
Add in the tomato puree, spice blend, turmeric, cinnamon and coriander and mix through, cooking until oil begins to separate.
Add in the marinaded chicken pieces and toss through the mixture, cooking for 3 minutes.
Add the tamarind into the sauce and balance with salt and sugar.
Add the water and allow to simmer until the curry becomes the consistency of thick gravy.
To quicken the thickening process, you can add in the cornstarch slurry.
Serve with rice and a quick raita.