Grease a 6" baking tin, preferably rectangular.

Start Preheating oven at 180 degrees C. Preheat it for 15 minutes and in the meantime, your batter will get ready.

Sift wheat flour, baking powder, baking soda and salt at least thrice for better aeration.

Take thick curd, oil, sugar and vanilla essence in a bowl and whisk for 3 to 4 minutes till sugar dissolves and everything comes together

Add flour mixture in the curd mix in 2 to 3 instalments. After each addition, lightly mix using cut n fold method. 

If the batter is too thick then adjust consistency by adding little milk. The batter should be of ribbon consistency

Now, divide the batter equally in 2 bowls.

In one bowl, add cocoa powder and mix lightly. Add little milk, if need be.

Add 1/4 teaspoon vinegar in each bowl and give it a quick mix.

Start putting the two batters alternatively. First, put a ladle full of vanilla batter. Then in the centre of this white batter put a ladle of chocolate batter. As you put the above layer the bottom layer will itself start spreading. On this put the white layer. Similarly, keep on putting the alternate layers till both the batter gets used up. And you will see beautiful white and brown layers

To make the flower pattern, take a toothpick and slide it lightly from one corner to the middle. Similarly, draw lines from different corners towards the middle. 

Bake for 30 to 35 minutes or till toothpick inserted comes out clean.

After 10 minutes, loosen the sides of the cake using a butter knife and invert the cake on a wire rack.

When cool, cut n enjoy.