Add passion fruit pulp and seeds to a blender with 250ml water and puree. Pass through a sieve to remove seeds.
Soak gelatine in 5 tablespoons cold water. Gently heat in a water bath and stir to dissolve completely.
Pour fruit mixture back into blender. Add condensed milk and measure out the double cream in the tin. Add to blender with dissolved gelatin. Blend till smooth.
Pour mixture into a wet 23cm tube cake tin and refrigerate for about 4 hours.