Preheat the oven to 115°C (240°F/gas mark 1/4)
To make the crème brûlée, place the egg yolks in a large bowl with 125g (4.5 oz) of the sugar and the vanilla seeds. Whisk for about 5 minutes, until pale and fluffy and the mixture holds a trail of the figure eight.
Meanwhile, place the cream, coconut milk and milk in a pan with the scraped out vanilla pod, then simmer gently until the mixture just comes to the boil. Remove the vanilla pod, then slowly pour the hot milk and cream into the yolk mixture, whisking continuously. Pass through a sieve into a clean bowl.
Using a ladle, divide the mixture into 6 x 120ml (4fl oz) small dishes or ramekins set in a baking tin filled with enough boiling water to come halfway up the sides of the ramekins (this is called a bain-marie). Cover tightly with foil and bake in the oven for 1 hour, until just set but still with a slight wobble in the middle. Remove from the oven and leave in the bain-marie, still covered with foil, for another 30 minutes before removing and allowing to cool completely. Transfer to the fridge and allow to set for at least 6 hours, or preferably overnight.