Preheat oven to 150C/130C fan forced. If using a conventional oven, position your rack in the lower third of the oven. Grease and line the base and side of a 7cm deep, 18cm (base size) round cake pan with baking paper, making sure the paper sits 5cm above the edge of the pan.

Place egg yolks, lemon rind and caster sugar into a large bowl and whisk until combined. Add the yoghurt and whisk until combined. Sift over flour and cornflour, and whisk until well combined.

Use electric beaters (or a stand mixer) fitted with a whisk attachment to whisk egg whites, lemon juice and salt in a clean, dry bowl until frothy. Gradually add the extra ⅓ cup caster sugar, in 3 batches, beating well after each addition to ensure the sugar is dissolved, until medium peaks form. Spoon a small amount of the egg white mixture into the egg yolk mixture and whisk until well combined. Use a spatula to carefully fold the remaining egg white mixture, in 3 batches, into the egg yolk mixture until no white streaks remain.

Spoon mixture into the prepared cake pan, smooth the surface, then place inside a baking pan. Pour enough boiling water into the baking pan to come 3cm up the side of the cake pan. Bake for 1 hour 10 minutes to 1 hour 20 minutes or until the top is light golden and the cake feels springy when touched in the centre. Turn off the oven and leave the cake to cool inside for 15 minutes with the door slightly ajar.

Remove the cake from the baking pan and set aside to cool in the pan until warm. Carefully turn the cake onto a serving plate top-side down, remove the paper lining and then quickly and gently turn top-side up. Set aside to cool completely.

Dust the cake with icing sugar, before cutting into wedges to serve.