Preheat oven to 160 degrees C. Grease and flour two 20x10cm loaf tins. Sift together the flour, baking powder and bicarb soda, set aside.
In a medium bowl, cream together the butter, white sugar, icing sugar and brown sugar until smooth. Add egg whites and egg yolk, beating after each addition. Stir in the vanilla. Stir in the dry ingredients alternately with the milk. Divide the batter evenly between the two pans.
Bake for 60 to 70 minutes in the preheated oven until a toothpick inserted in the centre of the cake comes out clean. Cool in the pan for 10 minutes before inverting onto a wire rack to cool completely.