Add vinegar to milk, and leave without stirring.
Prepare baking pan, grease with some oil/ butter/shortening using a pastry brush or butter paper, and evenly dust with flour, tap the pan inverted to dust off the extra flour.
Sieve together flour, cornflour, baking powder and baking soda in a dry bowl. Keep aside.
Beat in butter, oil, essence and sugar together until light and fluffy.
Add in yogurt and beat till a little more.
Fold in flour alternating with buttermilk in three turns.
Gently fold in all the flour until it forms a smooth batter. Do not overbeat the batter.
Transfer batter to cake pan and bake in a preheated oven for 35-40 minutes at 350°F or 180°C.
Once baked, take out from the oven, give it a 2-minute rest and transfer carefully to a cooling rack to completely cool it.