Preheat oven to 350°F. Line the bottom of the cake spring form with some parchment paper. Prepare one large and two medium bowls.
In a large mixing bowl, add eggs, salt and sugar. Beat on high for about 4-5 minutes or until the mixture doubles in size.
Add sour cream, melted butter, vanilla extract, flour and baking powder. Mix it again on the lowest speed until well combined.
Divide the cake batter between two medium bowls. In the first one, add the remaining 20 grams of flour and mix with a spatula. In the second bowl with the second half of the batter, add 20 grams of cacao powder and mix to combine. The batter should still remain pourable.
Pour two spoonfuls of chocolate batter into the center of the cake pan. Then, pour two spoonfuls of vanilla batter on top of the chocolate. Continue alternating spoonfuls of vanilla and chocolate batters, always pouring into the center. As you add more batter, it will spread out and fill the cake pan. Gently tap the pan on the counter to help the batter spread evenly.
After all the batter is added, use a knife or toothpick to draw four lines from the center of the cake to the edges, visually dividing it into four parts. Then, draw four more lines from the edges back to the center, creating eight even sections. This step is optional but adds a fun design to the cake.
Bake zebra cake at 350°F for about 40-50 minutes or until the toothpick comes out clear.
Let the cake cool down for about 20 minutes before removing it from the pan. You can serve it tight away. You can also dust it with sugar or add some frosting on top.