Put a roasting pan three-quarters full of water on the centre shelf of the oven and preheat the oven to 170°C/325°F/gas mark 3. Put the cream and milk into a saucepan and bring barely up to bubbling. Add the coconut milk powder and salt, remove from the heat and stir until dissolved. Put the eggs, egg yolks and caster sugar into a bowl and whisk together thoroughly. Then whisk the hot coconut cream into the egg mixture a little at a time.
Pour the mixture into a 1.2 litre/2 pint ovenproof dish and stand it in the roasting pan of water in the oven. Cook for 1-1¼ hours, until the custard feels set to a very light touch but still wobbles slightly. Remove from the oven and leave until cold. Serve at room temperature.