Preheat & prep: Preheat your oven to 350°F (175°C). Grease an 8×8 or 9×9-inch baking dish.
Make the cake batter: In a bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt. In a separate bowl, mix melted butter, eggs, vanilla, and milk. Combine wet and dry ingredients until smooth.
Pour & spread: Pour the batter into your prepared baking dish and smooth the top.
Add the pudding layer: In a small bowl, mix brown sugar and cocoa powder, then sprinkle evenly over the cake batter. Pour hot water gently over the top—don’t stir. Magic happens in the oven.
Bake: Bake for 35–40 minutes. Don’t panic if it looks a little gooey in spots—the pudding will set as it cools.
Cool & top: Let it cool for 15 minutes. Top with whipped cream, chocolate shavings, or berries.
Serve: Scoop generously, watch the pudding ooze, and try not to eat the whole pan yourself.