Put the passion fruit pulp into a large bowl with the yoghurt and stir well until evenly blended.

Sprinkle the gelatine over the water in a heatproof bowl and leave to soak for 5 minutes, then stand bowl in a pan of gently simmering water for 1 - 2 minutes until the gelatine has completely dissolved, stirring occasionally.

Cool the gelatine slightly, then pour on to passion fruit mixture,

stirring vigorously all the time to blend. Add the sugar and stir until dissolved.

Pour the mixture into an 850 ml (1 1/2 pint) metal or other freezerproof container. Leave, uncovered, in the freezer or freezing compartment of the refrigerator for 45-60 minutes until the mixture is frozen around the edges.

In a clean, dry bowl, whisk egg whites until standing in stiff peaks.

Turn passion fruit mixture into a large bowl and whisk until smooth and creamy, then fold in egg whites with a large metal spoon.

Return mixture to the container, cover tightly and freeze for a further 4 hours or until firm.

About 45 minutes before serving, transfer the mixture to the main part of the refrigerator to soften slightly. To serve: carefully scoop into individual glasses.