In a separate bowl, beat the butter with 1 cup (200g) of sugar until fluffy. Beat in the egg yolks one at a time.
Stir in the dry mixture alternately with the milk, until everything is evenly combined.
In a separate bowl, whip the egg whites with 1/4 sugar (50g) until stiff. Stir in one quarter of this mixture with the cake batter to lighten it up, and then gently fold in the rest of the whipped egg whites with the cake batter.
Scrape batter into the greased pan, and smooth out the top.
Bake in the preheated oven for 50-60 minutes, until a knife inserted in the centre comes out clean (cover loosely with foil if the top is browning too quickly).
Cool for 10 minutes before loosening the cake from the pan, and then allow to cool completely.