For the cake, whisk together the flour, sugar, cocoa, baking powder, coffee granules. In a separate bowl or measuring glass, combine the milk, melted butter, and vanilla and microwave for about 20 seconds. Pour the wet ingredients into dry ingredients.
For the hot fudge, add the sugars and cocoa powder to a bowl, then sprinkle the sugar mixture on top of the cake batter and spread it even.
Pour the boiling water on top. It should completely submerge the sugar mixture. Carefully transfer the skillet to the oven and bake for 25-30 minutes.
Allow the cake to cool for about 20 minutes. Then top with ice cream and serve right away. Enjoy!