Preheat the oven to 100°C/80°C fan. Split the vanilla pods and scrape out the seeds. Place the pod and seeds in a saucepan with the cream and milk and bring to the boil. Remove from the heat and set aside to infuse for 10 minutes.
While the milk infuses, divide the raspberries between 4 ramekins.
Beat the sugar and eggs together in a large heat-proof bowl until combined. Reheat the cream to simmering point then pour it in a thin steady stream on to the egg mixture, whisking continuously as you pour, until the mixture is smooth.
Strain the custard through a fine sieve into a large jug, then divide it evenly between the ramekins.Place the filled ramekins in a large deep roasting tin and pour enough hot water into the tin to come halfway up around the ramekins. Bake the custards for 30-35 minutes, or until just set and still a bit wobbly in the middle.
Remove the ramekins from the tin and allow to cool to room temperature.
When you're ready to serve, evenly sprinkle a layer of caster sugar over the surface of each custard, place on a flameproof surface such as a baking tray, then carefully caramelise the sugar using a blowtorch. For extra crunch, sprinkle over another layer of sugar and repeat this step.
Leave the crème brûlées to cool for a minute then serve.