Marble Cake

Directions

1. 1
   Preheat the oven to 180 degrees Celsius.
2. 2
   Line a 20 x 20 centimeter cake pan with parchment paper.
3. 3
   Beat the butter until light and fluffy. Mix in the sugar.
4. 4
   Beat in the egg yolks and milk until combined.
5. 5
   Sift in the flour and baking powder. Mix until just absorbed.
6. 6
   Separately, in a bowl whisk the egg whites with a pinch of salt until stiff peaks form. Carefully fold them into the first mixture.
7. 7
   Divide the batter in 2. In 1 half, add the vanilla. In the other half, add the cocoa powder.
8. 8
   Pour the 2 batters into the cake pan alternating batters. With a knife, insert the tip into the batter and swirl it around between the 2 batters.
9. 9
   Bake 20 minutes until a toothpick inserted in the center comes out clean.