Place cream, half the caster sugar and vanilla bean in a saucepan and bring gently to the boil. Remove from heat, cover and leave to sit for 10 minutes.
Lightly whisk yolks with remaining sugar. Gradually add hot cream, whisking well, then pour through a sieve into a clean jug.
Put four raspberries in the base of each ramekin and pour on the cream mixture. Place ramekins in the bain-marie and
Once cooked, turn the oven off and very carefully take the bain-marie from the oven (the roasting dish is full of very hot water, so be careful). Remove ramekins from the bain-marie and cool on a wire rack for 30 minutes. Refrigerate, covered, for 4 or more hours until they have set firm.
Just before serving, sprinkle demerara sugar in a thin layer on top of each brûlée. Place under a very hot grill, or use a cook’s blowtorch, until a thin layer of caramel forms. Keep an eye on them as they will go from sugar to burnt toffee quite quickly. Stand 1 minute before serving, as the toffee will burn your lips.