1. Preheat the oven to 180°C (350°F) and grease and flour a cake tin.
2. In a large bowl, sift the 3 cups of flour along with the baking powder. Reserve this mixture.
3. In another container, beat the eggs and add the sugar. Continue beating until you obtain a foamy, lighter-colored mixture.
4. Add the melted butter and milk to the egg and sugar mixture. Add the teaspoon of vanilla sugar or essence and mix well.
5.  Gradually add the flour and baking powder mixture. Mix until you obtain a homogeneous mass.
6. Divide the dough into two equal parts. In one of them, add the cocoa powder and mix until you obtain a chocolate mass.

bottle trick

1. Place half of a plastic bottle in the center of the mold, mouth side down. Pour just a little of the vanilla batter into the mold and then pour just a little of the chocolate batter over the bottle. Repeat the operation until the mixture is finished.
2. Finally, very carefully remove the plastic bottle.
3. Place the pan in the preheated oven and bake for approximately 45-50 minutes, or until a toothpick inserted into the center comes out clean.
4. Let the cake cool in the pan for about 10 minutes before transferring it to a wire rack to finish cooling.

And there you have it! You will be surprised by the pattern that has formed. A marbled sponge cake with a magical touch that will make everyone wonder what the secret is behind its exquisite pattern. Serve this unique dessert on any special occasion and enjoy the compliments you will receive for this incredible creation. To enjoy!