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.
Chocolate Icing
Mix together icing sugar, cocoa powder.
Add butter and boiling water.
Mix together till you get a smooth mixture is formed.
Assembling Lamingtons
In a flat dish plate take desiccated coconut.
Cut cake into desired pieces.
Dip in chocolate icing/sauce.
Then carefully roll into coconut.
Notes
You can use All purpose flour instead of Whole Wheat Flour. or take equal amount of both the flours. Omit Cornstarch then.Instead of butter you can add any flavorless plant based oil like Olive oil or Rice Barn oil.