Preheat oven to 400 degrees. Spray a baking pan and set aside
In a large bowl mix these dry ingredients together: sugar, flour, salt and baking soda and set aside.
In another bowl mix together the milk, eggs, vanilla essence and vinegar. Whisk together.
In a saucepan mix the butter and cocoa powder until fully melted and combined. Now add this to the flour mixture and mix well.
Now add the milk, eggs, vanilla and vinegar to this and mix till well combined.
Pour into the pan and bake for 30 minutes or until a toothpick inserted in the middle comes out clean.
Icing:
Start making the icing right before the cake is done baking.
In a saucepan mix together the butter, cocoa powder and milk. Mix and let boil. Reduce the heat, add the sugar and vanilla. Mix well and take off heat.