grease with butter or oil and line the cake pan with parchment paper.
sift the flour and baking powder.
add salt with the flour and mix and set aside.
in another bowl sift the cocoa powder.
make a paste with sifted cocoa powder, 1 tbsp sugar and 1/4 cup milk.
preheat oven at 180 degree celsius temperature.
beat the butter with sugar until creamy.
add eggs one at a time and mix until well combined.
add vanilla essence and mix well.
alternatively add milk and flour mixture until all is well incorporate on low speed of your beater.
take 2 cups of the batter and mix along with the chocolate mixture.
use one or two or three tablespoons of each batter (chocolate and white) to create the pattern on the prepared cake pan.
start from middle of the pan.
take one or two or three spoonful of white batter, then add one or two or three spoonful of chocolate batter over it.
repeat this steps until all of the batter has been used.
bake the cake for 35-45 minutes in the centre of the pre-heated oven or until the cake is lightly brown.
depending on oven, time may take bit less or more. Insert a toothpick middle of the cake, if it's come out clear, then it's perfect. If not, then need bit longer time.
cool the cake in the pan for 10 mins, then turn out in a wire rack.
After completely cool down, frost the cake as you wish.