Preheat your oven to 350°F and lightly grease an 8×8-inch baking dish. This dessert works best in a smaller baking dish because it helps create a deep, rich fudge layer underneath the cake.

In a medium bowl, whisk together the flour, granulated sugar, cocoa powder, baking powder, and salt until evenly combined.

Add the milk, melted butter, and vanilla extract to the dry ingredients. Stir gently until a thick chocolate batter forms. Avoid overmixing because it can make the cake layer dense instead of soft and fluffy.

Spread the batter evenly into the prepared baking dish using a spatula.

In a separate bowl, combine the brown sugar and cocoa powder for the topping mixture. Sprinkle this evenly over the cake batter. Do not stir.

Carefully pour the hot water over the entire surface of the cake. It may look unusual at first, but this step is what creates the rich hot fudge sauce underneath while the cake bakes.

Place the dish carefully into the oven and bake for 35 to 40 minutes. The top should look set and cakey while the bottom stays soft and fudgy.

Allow the cake to rest for about 10 minutes before serving. As it cools slightly, the fudge sauce thickens into a rich molten chocolate layer.

Spoon the warm cake into bowls, making sure to scoop some of the hot fudge sauce from the bottom of the pan with each serving.

Top with vanilla ice cream and extra chocolate syrup for the ultimate dessert experience.