Combine sugar, water, cinnamon and cardamom in a medium saucepan and stir over medium heat until sugar dissolves. Bring to a simmer, add plums and gently simmer for 5 minutes or until just tender. Remove from heat and set aside.
To make the yoghurt cream, place the cream, yoghurt and icing sugar in a bowl and whisk to combine.
Divide warm plums between bowls, removing their skins as you go. Serve with some of the syrup and a dollop of yoghurt cream.