- Preheat the oven to 180°C
- Grease, line and lightly flour a 20cm spring form cake pan. Dust out excess flour and keep it aside.
- Heat the butter in a saucepan, over low heat. Add the milk, sugar and a pinch of salt and stir until the sugar dissolves. Turn off the heat, sift in the cake flour, add the egg yolks and vanilla and mix by hand, until just combined.
- In a separate bowl, whisk the egg whites until foamy, and add the lemon juice and sugar a little bit at a time, beating until stiff peaks form. Add about 2 tablespoons of the meringue mixture into the batter mixture.
- Mix until just combined, and then pour this combined batter into the remaining meringue mixture. Gently fold this batter until combined. Do not stir or whisk vigorously, just fold in.
- Pour the batter into the greased and lined cake pan. Tap the pan on the countertop a few times and get the air bubbles out.
- Prepare a water bath by pouring cold water into a large oven pan. Place the cake pan containing the batter into the large roasting pan. The water in a large baking pan should reach 2 ½ cm up the sides of the cake pan. Bake for 25 to 35 minutes or until the cake is firm and set in the centre. If you find that the cake is browning too quickly, cover it loosely with foil.
- Once baked, remove from the oven and water bath. Leave the cake in the pan to cool for about 10 minutes before gently turning it out.
Cool completely, and dust with powdered sugar or cover with a topping of your choice.