Separate the egg whites from yolks and whip the egg whites with a pinch of salt. Put then in the fridge.
Whip butter and sugar in a cream with electric whisk for about 2 minutes. Add the yolks and keep on whipping pouring later, little by little, the sifted flour, alternating with milk. Combine the whipped egg whites to the mixture and mix gently from bottom to top and then add the baking powder for cakes and mix. Pour the mixture into a cake pan of 24/26 cm in diameter, suitably greased and floured. Bake at 180 °C for about 40 minutes. Remove from oven and allow to cool well before removing it from the mould. Dust with icing sugar.