Preheat oven to 180°c.grease and lightly flour 24 cm ring tin;tap out excess flour.

Sift the flour and  baking powder in to a bowl.

Beat butter and sugar until smooth and fluffy.beat in egg yolks one at a time.transfer mixture to large bowl ;stir in flour and butter milk.

Beat egg whites in small bowl with electric mixer until soft peaks form.fold in to cake mixture.

Transfer the mixture in to prepared pan,bake cake about 40 minutes.

Buttermilk:-fresh low fat milk cultured to give a slightly sour,tangy taste; low fat yogurt or milk can be substituted.