Preheat oven to 150°C. Put the cream into a small saucepan, add vanilla bean pod and seeds. Place over medium-low heat until almost simmering (90°C).
Meanwhile, place egg yolks and caster sugar in a bowl and whisk by hand until pale and creamy, then add in the juice. Pour hot cream over egg mixture, whisk to combine, then strain.
Line a deep roasting tray with paper towels. Divide cream mixture between four 1-cup-capacity ramekins, and place the ramekins into the tray. Fill tray with hot tap water until halfway up ramekins and cover with foil, piercing a few holes in the top. Bake for about 50-55 minutes until just set, remove ramekins from tray and set aside to cool. Place in fridge for at least 3 hours before serving.
To serve, sprinkle the demerara sugar on the brûlée, taking care to remove any excess, and caramelise using a blowtorch.