Sieve wheat flour, cocoa powder and baking soda together for 5-6 times and keep it aside.
Take milk and add sugar to it. Mix it till sugar is dissolved completely.
Now add oil, vineger and vanilla essence.
Mix till it is nicely combined and keep it aside for 5 minutes.
Add the dry ingredients to wet mixture in batches and combine without forming lumps.
Grease the tin with butter and dust it with little flour.
Fill the tin till ¾ and tap to release air.
Heat pan and place plate with holes in it, close the lid and preheat for 5 minutes.
Then place the cake tin in the kadai.
Close it with lid and bake in low flame for 45-50 minutes till tooth pick inserted comes out clean.
Allow the cake to cool down completely and then slice as pieces and enjoy.
Chocolate sponge cake is ready.