Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking dish to prepare it.
In a mixing bowl, combine the flour, sugar, cocoa powder, baking powder, and salt. Mix them well.
Stir in the milk, melted butter, and vanilla extract until everything is smooth and well combined.
Pour the batter into the prepared baking dish.
In a separate bowl, mix the hot water and brown sugar until dissolved. Pour this mixture over the batter, but don’t stir it in!
Bake in the oven for 30-35 minutes until the top is set and you see the fudge sauce bubbling.
Allow it to cool for a few minutes before serving. It’s amazing on its own or topped with ice cream!