Step 1: Preheat the Oven

Preheat your oven to 180°C (350°F). Grease and line the bottom of two 20cm (8-inch) round cake tins with parchment paper.

Step 2: Whisk the Eggs and Sugar

In a heatproof bowl, crack the eggs and add the caster sugar. Place the bowl over a pan of simmering water (double boiler), ensuring the water doesn’t touch the bottom of the bowl. Whisk the eggs and sugar constantly until the mixture becomes warm to the touch and the sugar is fully dissolved, about 3-4 minutes.

Step 3: Whip Until Fluffy

Remove the bowl from the heat and continue to whisk using an electric mixer or hand whisk on high speed. Whisk for about 5-7 minutes until the mixture triples in volume, becomes pale, and forms ribbons when lifted. The batter should be light and fluffy.

Step 4: Fold in the Flour

Sift the plain flour and a pinch of salt over the egg mixture, and gently fold it in using a spatula. Be careful not to deflate the air that was whisked into the eggs. Add the vanilla extract (if using) during this stage.

Step 5: Fold in the Melted Butter

Once the flour is fully incorporated, gently fold in the melted butter. Be careful to fold slowly to avoid knocking out the air.

Step 6: Pour into Tins and Bake

Divide the batter evenly between the two prepared cake tins. Gently smooth the tops with a spatula and place the tins in the preheated oven. Bake for 20-25 minutes or until the cakes are golden and spring back when lightly pressed. A skewer inserted into the center should come out clean.

Step 7: Cool the Cakes

Remove the cakes from the oven and allow them to cool in the tins for 5 minutes. Then, turn them out onto a wire rack to cool completely before filling or decorating.