Preheat oven to 180°C. Lightly grease and line a 10x20cm loaf pan. Place butter and caster sugar in a large bowl and beat with electric beater until light and creamy. Add lemon rind and lime rind. Add eggs, one at a time, beating between each addition until the mixture is well combined. Fold flour and desiccated coconut into the mixture, alternating with milk, until just combined. Spoon the mixture into the lined pan and smooth the surface. Bake for 45-50 minutes or until golden and a skewer inserted into the centre comes out clean. Dust with icing sugar. Serve cake warm or at room temperature, with a spoonful of Greek-style yoghurt.