To make the cake batter, add the milk, oil and granulated sugar to a bowl. Whisk together to combine
Sift in the flour, cocoa powder, baking powder and salt. Whisk again until the dry ingredients are just combined and no lumps remain; do not overmix
Pour the cake batter into a microwave-safe deep casserole dish that is 7x11" or a similar size (e.g., 9x9", 8x11") and ideally 3" deep. No need to line or butter the dish because the cake will be served straight from it
In another bowl, mix together the cocoa powder, granulated sugar and brown sugar for the pudding sauce. Sprinkle the cocoa mixture on top of the cake batter in the casserole dish
Bring 1 cup of water to boil, and very carefully and gently pour it on top of the cocoa mix in the casserole dish. This water will help create the hot fudge pudding sauce as the cake cooks in the microwave
Carefully transfer the dish to the microwave. Microwave on high for 7 to 8 minutes until the cake looks done on top. If in doubt, it is better to slightly undercook than overcook, as overcooking will cause the cake to become dry
Let the cake cool down for ~10 minutes, then scoop it out along with the fudge sauce underneath and serve with vanilla ice cream!
