Preheat the oven to 180°C. Line a 22cm or 23cm round cake tin with baking paper. Place the caster sugar, eggs, yoghurt, oil and lemon zest in the bowl of an electric mixer. Mix on low speed until the mixture is just combined. Sift in the self-raising flour, then mix until just combined. Pour the cake mixture into the prepared tin and place in the oven to bake for 40–45 minutes or until a skewer inserted in the centre of the cake comes out clean. Remove from the oven.
In a small bowl, mix together the caster sugar and lemon juice until the sugar dissolves. Spoon the syrup over the hot cake and leave to cool in the tin.
Mascarpone elderflower icing
Place the mascarpone, cream cheese and icing sugar in a bowl and mix gently using a wooden spoon or spatula to combine. Add the elderflower cordial and gently stir through.
Remove the cooled cake from its tin and place on a serving plate.