In a large microwave-safe mug or dish, whisk together all-purpose flour, caster sugar, cocoa powder, and baking powder
Stir in milk, neutral oil or melted butter, and a splash of vanilla until you have a glossy batter
Sprinkle brown sugar and cocoa powder evenly on top of the batter without mixing
Pour hot water over the sugar and cocoa powder mixture without stirring into the batter
Microwave for 1.5 minutes or until the cake seems set, being careful not to over-cook
Scoop ice cream on top and serve immediately
