Preheat the oven to 150C/300F/Gas 2.
Bring the cream and milk to a simmer in a heavy-based pan over a medium heat.
Add the vanilla seeds and pods and stir well to combine.
Whisk together 75g/2½oz of the caster sugar and all of the egg yolks in a large mixing bowl until pale, fluffy and well combined.
Remove the vanilla pods from the milk and cream mixture. Pour the warm milk and cream mixture over the whisked egg and sugar mixture, stirring continuously until the sugar has dissolved.
Pour the crème brulée mixture into four ramekins. Place the ramekins into a deep-sided roasting tin. Carefully add enough boiling water to the roasting tin to reach halfway up the sides of the ramekins. (This is called a bain-marie.)
Transfer the bain-marie to the oven and cook for 30-35 minutes, or until the custard has set firm but still has a slight wobble. Remove the crème brulées from the bain-marie and set aside to cool.
Once cool, chill the crème brulées in the fridge until needed.
When the crème brulées are ready to serve, sprinkle 20g/¾oz of the remaining caster sugar onto the surface of the crème brulées. Using a chefs' blowtorch, heat the sugar until it melts and caramelises, then set aside to cool.
Repeat the process with the remaining sugar, until the sugar has caramelised and hardened. Serve immediately.