Preheat the oven to 180°C. Spray a 23-cm cake tin with cooking spray.
Combine the butter and 1 cup of the sugar in a large bowl. Beat with an electric mixer until light and creamy. Add the eggs one at a time, mixing well after each addition. Stir in the yoghurt, ¼ cup of the lemon juice, the grated lemon zest, flour and bicarbonate of soda and mix well.
Spoon the mixture into the prepared tin and bake for 45 minutes or until a skewer inserted in the centre of the cake comes out clean.
Meanwhile, combine the remaining sugar, lemon juice and ½ cup water in a small saucepan. Cook, stirring, over low heat until the sugar has dissolved, then add the julienned lemon zest and simmer for 4 minutes.
Remove the cake from the oven and pour the zest and syrup over the top while the cake is hot and still in the tin. Let the cake stand for at least 5 minutes before serving in slices with some extra yoghurt, if desired.