Preheat oven to 350 degrees F. Grease and line an 8x4 inch loaf pan and set aside.
Combine milk and vinegar in a cup.
Stir and set it aside for 5 to 10 minutes until it curdles.
Combine the flour, cornstarch, baking powder, baking soda, and salt.
Sift the dry ingredients through a sieve to remove all foreign particles and break up lumps. Sifting also helps the dry ingredients to distribute evenly in the batter.
Using the paddle attachment of your electric mixer or hand mixer, blend together oil and sugar until you achieve a creamy consistency.
Beat until light and fluffy, 3 to 5 minutes.
Once that creamy consistency is achieved, add vanilla essence ( to the oil + sugar mix) to create that irresistible aroma. Pour in buttermilk.
Now, add in the sifted dry ingredients and mix. Remember not to overmix.
Stop mixing when the batter is just barely combined.
The batter should be of a dropping consistency.
Take out ⅓ of your batter, combine it with the cocoa powder, and fold it gently until the cocoa goodness melds harmoniously with the alluring flavors of vanilla.
Layer your batter into your pan, starting with vanilla.
Then, spoon the chocolate batter over it- alternating between the two until all the batter is used up.
Finally, end the top layer with vanilla batter.
Use a butter knife or a toothpick to swirl them together gently for a marbled appearance. Tap the pan firmly on the counter. Tip — Tapping releases the steam from the cake, thus preventing it from shrinking. Bake at 350°F for 30-35 minutes, or until the toothpick inserted in the center comes out mostly clean but with a few moist crumbs.
Allow the cake to cool for 15 minutes before carefully inverting it onto a wire rack to cool completely.
Slice the cool cake into pieces.
And enjoy with a cup of warm tea or coffee. This cake not only delights the palates but also warms the heart with its enchanting swirls and exceptional flavors.