Preheat the oven to 150°C, fan 130°C, gas 2. Place the sugar and egg yolks in a large bowl and whisk until pale and fluffy.
Pour the cream into a saucepan, then add the vanilla seeds and pod. Bring to the boil, then remove from the heat and discard the pod. Add to the egg mixture, whisking continuously, then strain through a fine sieve into a jug.
Pour the mixture into 6 x 150ml ramekins, filling almost to the top. Place them in a deep roasting tin and pour in enough hot water to come halfway up the sides. Bake for 30-35 minutes, until just set but still a bit wobbly in the middle. Remove from the water and leave to cool, then chill in the fridge for 2-3 hours.
Before serving, preheat the grill to hot. Sprinkle the top of each custard with 1 teaspoon sugar, then place under the grill to caramelise. When a thin layer of caramel forms, sprinkle on the remaining 6 teaspoons sugar and grill again to form a thick, crunchy layer. Serve when the tops have cooled and hardened.