Photograph: Kate Whitaker
Heat 400ml of the cream to boiling point with the vanilla pod and lemon rind; simmer until the liquid has reduced by a third. Remove from the heat, pour into a large bowl and leave to cool over ice. Soak the gelatine in the milk for 10 minutes until soft, then remove the gelatine and reserve. Gently heat the milk until just below boiling point.
Return the softened gelatine to the milk and stir until dissolved. Add the milk to the cream, vanilla and lemon mixture and stir to combine. Strain into a bowl to remove the lemon zest and vanilla pod. Cool, whisking every 5 minutes to prevent it from going lumpy.
Whip the remaining 200ml of cream in a bowl with the icing sugar. Once the lemony cream has cooled and is the consistency of double cream, fold in the whipped cream.
Pour the mixture into a lightly oiled 600-750ml fluted jelly or dessert mould, cover and leave the panna cotta to set in the fridge for at least 3 hours.
To serve the panna cotta, immerse the mould in a bowl of boiling water for 5-10 seconds, then invert on to a plate. Scatter with raspberries and pomegranate seeds.
You can prepare the panna cotta to the end of step 4 up to 2 days ahead.