Preheat the oven: Set your oven to 180°C (160°C fan)/350°F/gas mark 4.

Prepare the tins: Grease and line two 20cm round cake tins with baking parchment.

Set up a bain-marie: Place a heatproof bowl over a pan of simmering water (making sure the bowl doesn’t touch the water).

Whisk the eggs and sugar: Crack the eggs into the bowl and add the caster sugar. Using an electric whisk, beat the eggs and sugar continuously over the heat for about 5-7 minutes, until the mixture is pale, thick, and has tripled in volume.

Remove from heat: Once the egg mixture is thick and holds its shape, remove it from the heat.

Fold in the flour: Sift the plain flour and salt over the egg mixture and gently fold it in using a spatula. Be careful not to deflate the batter.

Add the melted butter: Drizzle the cooled melted butter and vanilla extract (if using) into the batter, gently folding until fully incorporated.

Divide the batter: Evenly divide the batter between the two prepared tins and smooth the tops with a spatula.

Bake: Place the tins in the preheated oven and bake for 20-25 minutes, or until the cakes are golden and springy to the touch.

Cool the cakes: Allow the cakes to cool in the tins for 10 minutes before turning them out onto a wire rack to cool completely.

Layer with your favorite fillings: Once the cakes are completely cooled, you can layer them with whipped cream, fruit, or buttercream.

Dust with icing sugar: For a simple finish, dust the top of the cake with icing sugar before serving.