For the spice mix, grind the spice mix ingredients to a paste using a mortar and pestle. Set aside.
For the coconut chicken curry, season the chicken pieces, to taste, with salt and freshly ground black pepper.
Heat two tablespoons of the oil in a large, heavy-based saucepan or deep-sided casserole over a medium heat. Add the seasoned chicken pieces and fry for 3-4 minutes, turning regularly, or until browned on all sides. Remove from the pan and set aside (keep warm).
Heat the remaining two tablespoons of oil in the same pan, then add the onions, butternut squash, aubergines and potatoes, in batches if necessary, and fry for 4-5 minutes, stirring regularly, or until just softened and pale golden-brown.
Add the spice mix to the pan and stir well to coat the vegetables. Continue to cook the mixture for 3-4 minutes, stirring well, or until the spices are fragrant.
Return the browned chicken pieces to the pan and add the coconut milk, chicken stock, tamarind paste and bay leaves. Stir well and bring the mixture to the boil, then reduce the heat until the mixture is simmering. Cover the pan with a lid and continue to simmer for 35-40 minutes, or until the chicken pieces are tender and the sauce has thickened.
Add the mango, papaya, lime juice and rum (if using), stir the mixture well, then cover and continue to simmer for 4-5 minutes, or until the fruit has warmed through.
To serve, divide the rice equally among six serving plates. Spoon over the coconut chicken curry.