In a mixing bowl add all purpose flour, baking powder, baking soda and salt.
Sieve it a couple of times until the flour is mixed well with the leavening agents.
In a smaller mixing bowl, add dutch processed cocoa powder and add 4 tbsp of hot water. Mix it well so that there are no lumps. It should look glossy.
In another mixing bowl add curd, vanilla essence and castor sugar and mix it well until the sugar is dissolved.
Next add oil and whisk it until it is incorporated into the curd mix.
Now add few spoons of the flour mix and fold it in gently.
Pour some of the milk and fold it in too.
Repeat the above two steps starting and ending with flour mix. Now the cake batter is ready.
Add 1/3rd of the prepared cake batter to the cocoa mix. Fold it in gently making sure it is mixed well.
Meanwhile preheat the oven at 180°C for 10-15 mins. In a greased and lined 9x5inch loaf fan, add a layer of vanilla cake batter.
Add 2-3 tbsp of chocolate batter over the vanilla cake batter. Using a skewer, create marble effect going all the way to the bottom. Don’t overdo the marble effect, that would just mix both the colors together and not create marble effect.
Add the vanilla and chocolate batter alternatively, creating marble effect as you go. The top layer should be chocolate and you mix it, just dip the skewer 1” into the cake batter.
Bake the cake at 180°C for 40-45 mins until it is golden brown and a tester comes out clean. Rest for 5 mins and remove it from the loaf pan, cool it down on wire rack.
Slice and serve with a cup of tea/coffee. Cake can be refrigerated for about a week in an airtight container.