01 -
Preheat your oven to 350°F (175°C).
02 -
In a large bowl, combine the flour, sugar, cocoa powder, baking powder, and salt. Mix well. Add the milk, melted butter, and vanilla extract. Stir until the mixture forms a smooth batter. Fold in chopped nuts, if using.
03 -
Pour the prepared batter into a greased 9x9-inch baking dish or a similar-sized oven-safe dish.
04 -
In a small bowl, combine the brown sugar and additional cocoa powder. Sprinkle this mixture evenly over the top of the batter.
05 -
Carefully pour the hot water over the top of the cake without stirring. The water will sink to the bottom and create a fudge sauce while the cake bakes.
06 -
Bake for 35-40 minutes, or until the cake has risen and the top looks set, while the fudge sauce is bubbling underneath.
07 -
Let the cake cool slightly before serving. Serve warm with a scoop of vanilla ice cream or whipped cream, if desired.