Place 110g (1/2 cup) of sugar in a saucepan with 100ml water. Bring to the boil over high heat, and then turn heat to low and simmer for 2-3 minutes. Allow to cool.
In a large bowl, beat egg yolks with an electric mixer until pale. Slowly add cooled sugar syrup. In a separate bowl, whip cream until soft peaks form and fold in egg mixture, yoghurt and lemon rind.
Spoon into 6 lightly greased dariole moulds*, and freeze for at least 4 hours, or until firm.
Place remaining sugar and 1 cup of water in a saucepan. Stir over low heat until dissolved, and then simmer for 5 minutes.
Add orange juice to sugar syrup, simmer for a further 2 minutes, and then cool completely.
To serve, spoon orange syrup over parfaits, and garnish with season berries and a spring of mint if desired.