Preheat oven to 160ºC/325ºF/gas mark

Grease a 20cm/8-inch square cake tin

Separate the eggs

Add egg whites to a food mixer, using the whisk attachment, whip until stiff and forming peaks

Spoon the whites into another bowl and set aside

Clean the mixer bowl, add the egg yolks and caster sugar and beat until light

Add the butter and vanilla extract to the mixture and continue beating for another minute or two

Add the flour until combined well

Gradually add the milk, beating until well combined

Add the egg whites in three stages, gently folding them into the mix using a spatula or metal spoon

Carefully pour the batter into the cake tin and cook for 40-50 minutes or until the top is lightly golden

Allow to cool in the tin

Once the cake has completely cooled, lightly sprinkle icing sugar over the top, slice and serve