Preheat the oven to 350˚F. In a medium bowl, stir together the flour, sugar, cocoa, baking powder and salt. In a small bowl or measuring cup, stir together the milk, oil and vanilla (no, there’s no egg); add to the dry ingredients and stir just until combined. Spread into a buttered or parchment-lined 23 centimeter square pan or baking dish.
In the same bowl, stir together the sugars and cocoa, then stir in the hot water or coffee; pour over the batter, but don’t stir the two together. Bake for 20 minutes, or until the cake is springy to the touch and there’s a thick chocolate sauce underneath. Serve warm, with vanilla.