1. To make the sponge cake...
Preheat the oven to 350 deg Fahrenheit (170 to 180 deg Celsius).
Line one (or two if you don't want to cut the cake in half later) 7-8 inch (18cm) tin
with parchment paper and grease the tin with butter.
Start beating the egg whites, and then they get foamy add the granulated sugar in
2-3 portions. Beat until stiff peak.
Add the egg yolks to the egg white mixture and gently whisk until incorporated.
Add the milk, melted butter, vanilla extract, and flour (in that order) to the batter.
Gently fold until well combined. (Be careful, if you overmix the cake will come out
tough and not fluffy).
AS SOON AS YOU CAN (you don't want batter to deflate)- pour the batter into the
cake tins, give it one or two drops on the counter to get rid of the bigger air bubbles
and put it into the oven.
Bake the cake for 25-30 minutes. The cake will bring back to the touch when ready.
Let the cake cool in tin on the wire rack, then remove.