Preheat oven to 180 C fan forced (360 degrees F). Grease and flour a 9x13-inch baking pan.
Place flour, baking powder, and salt in a medium sized bowl. Mix together with a fork.
Place eggs in a large bowl and beat with an electric whisk or a stand mixer on high speed until lemon coloured.
Gradually add sugar, and continue beating until the mixture is thick, about 5 minutes.
Fold in the flour mixture using a spatula.
In a small microwave-safe bowl, warm up the milk till small bubbles form at the edge. Stir in the butter, and vanilla essence.
Add the milk and butter mixture to the batter, and lightly combine. This can be done with a spatula, or an electric whisk on low speed. Make sure you don’t overbeat.
Pour the batter into a prepared pan, and bake in a pre-heated oven until a toothpick or skewer inserted in the center comes out clean, 25 to 30 minutes. Let the sponge cake cool for a few minutes, and then take it out on a wire rack to cool completely.
This recipe makes a large cake – you will need about 75 – 80% for the trifle / ice box cake. The rest of the cake can be eaten (it’s delicious with a cup of tea), or you can make extra whipped cream, and make an additional small trifle / ice box cake.