Try this delicious cake recipe:
Beat butter and sugar with a little bit of salt, vanilla and lemon. Add whole egg and milk little by little. Sift flour, starch flour and baking powder and beat with the quantity.
Take 1/3 of the dough and mix it with the sifted cocoa and rum. Pour the dough into a greased and floured loaf pan in three layers (light, dark, light), spread smoothly and prick the dough a few times with a fork.
Bake the marble cake at 200 degrees for about 25 minutes. After a narrow, light brown pastry crust has formed, score it with a damp kitchen knife and finish baking the cake at 180 degrees for about 45 minutes.