Make sure your microwave is at full power.
Take a microwave safe dish and lightly grease it (this allows the parchment to stay in place). Add parchment paper and grease the parchment paper too.
Sift all the dry ingredients through a sieve in a large bowl - all purpose flour, cocoa powder, salt, baking soda- and break any large lumps if present.
Then add the sugar directly to the dry ingredients.
Using a WHISK, mix the dry ingredients very well.
In another bowl, put together the wet ingredients- oil, buttermilk, hot water and vanilla essence.
Again using a WHISK, mix the wet ingredients well.
Pour the wet ingredients into the dry ingredients.
Now using a SPATULA, slowly mix the batter and scrape the sides and bottom. Do not mix vigorously and do not overmix!
Pour the mixture into the prepared dish.
Place the dish in the microwave and set the timer for 5 minutes.
Once done, check for doneness by inserting a toothpick in the center. There should be a few crumbs on it.
Wearing oven mitts, very carefully remove the dish and let it cool completely.
To get nice neat cuts, refrigerate it for 30 minutes after it has cooled.
Any leftovers can be refrigerated.