First, in a microwave-safe mug ( roughly 1 cup measurement) mix together the sugar, milk and the vanilla essence until the sugar dissolves. (here you can also use white granulated sugar instead of brown, but brown sugar gives the brownie a nice chewy texture).
Then add in the oil, flour, cocoa powder, and the salt.
Mix all the ingredients until well incorporated.
Now microwave for 1 minute. (here I've used a 1200w microwave, if yours is different then the timing may vary. If the microwave you have is less than 1200w, it may take you up to 1.5-2 minutes to cook the brownie).
Take it out of the microwave oven and let it cool for a couple of minutes.
Serve the warm brownie with whipped cream or vanilla ice cream and enjoy!