Put the chicken pieces on a large plate and rub them all over with the lemon juice. Set aside for 20 minutes, then pat dry with kitchen towels.
Mix the salt, cayenne and flour together on a second plate and roll the chicken pieces in it, shaking off any excess.
Melt the butter in a frying-pan. Add the chicken pieces and fry until they are evenly browned. As they brown, transfer the pieces to a plate.
Add the onions, garlic, ginger and cumin seeds to the pan and fry until they are golden brown. Stir in the yogurt, cream and lemon rind. Return the chicken pieces to the pan and turn in the mixture to coat thoroughly. Bring to the boil, reduce the heat to low and cover. Simmer the chicken for 1 hour, or until it is cooked through and tender. Uncover the pan for the last 20 minutes to allow the sauce to thicken somewhat.
Discard the lemon rind and transfer the chicken and sauce to a warmed serving dish. Serve at once.