To start, gather your ingredients: all-purpose flour, unsweetened cocoa powder, sugar, baking powder, salt, milk, vegetable oil, and vanilla extract.
Preheat your oven to 350°F (175°C) and grease a baking dish.
In a mixing bowl, combine the dry ingredients—flour, cocoa powder, sugar,nut, baking powder, and salt. In a separate bowl, whisk together the wet ingredients—milk, oil, and vanilla—and then gradually incorporate them into the dry mixture, stirring until just combined.
Pour the batter into the prepared dish, 9" square pan, and sprinkle a mixture of cocoa powder and sugar on top. Finally, pour hot water over the cake batter without stirring.
As it bakes, the cake will rise and create a luscious chocolate pudding layer beneath.
Bake for about 30 to 35 minutes, or until the top is set. Once out of the oven, allow it to cool slightly before serving.