Preheat your oven to 350°F (175°C). Grab an 8-inch square baking dish – no need to grease it.
In a mixing bowl, stir together the flour, baking powder, salt, 3 tablespoons of cocoa powder, and 3/4 cup of the sugar.
Add in the milk, melted butter, and vanilla. Mix until the batter looks like thick chocolate pudding.
Pour this into the ungreased baking dish and spread it evenly. Trust the process.
In a small bowl, mix the remaining 4 tablespoons of cocoa powder with the remaining 1/2 cup sugar and the brown sugar. Sprinkle this mixture over the batter.
Pour the hot water gently over the top – don’t stir it! Yes, it’ll look weird. Yes, you’re doing it right.
Bake for 35 minutes. The top should be set, but underneath will be a gooey, rich sauce.
Let it cool for just a bit, then serve warm with vanilla ice cream. Or straight from the dish. We’re not judging.