Begin by deseeding the passion fruits. Press the seedy pulp through a plastic sieve, making sure it is only the black seeds that remain in the sieve and all the juice has been pressed through.
In a bowl, whisk together the eggs, egg yolks, sugar and juice until well combined. Heat the double cream and milk, and once almost boiling remove. Pour on top of the egg mixture, whisking all the time.
Return the custard to the pan and heat on a very low heat, again whisking constantly to prevent it turning into scrambled eggs. It should begin to thicken after ten minutes. It should be thick enough to coat the back of a spoon well.
Remove from the heat and divide into small ramekins or, alternatively, a single large serving dish. Set in the fridge overnight.
No more than two hours before serving, sprinkle the tops of the crème brulees with a layer of caster sugar. Use a blowtorch or grill to caramelise the tops. You should be able to tap a spoon on top of the caramel and get a very satisfying sound!