Pre-heat oven to 350°F or 180°C.
Sieve together flour, cornstarch, baking powder. Add salt if using unsalted butter.
Beat together butter, sugar and vanilla essence.
Add egg one by one and mix lightly.
Fold in flour in 3 parts, add milk/buttermilk alternatively.
Transfer cake pan and bake in preheated oven for 35 mins.
After 35 mins, check out whether cake is cake by toothpick test. Also, cake will sides of pan.
Take out of oven and then after 2-3 minutes, carefully transfer to cooling rack.
Once completely cool, freeze the cake for an hour, take out and cut into pieces.