Preheat the oven 170 C. Grease three ramekins that are at least 2 inches tall and 3.5 inches wide.
Combine the melted butter, milk, egg and vanilla in a mixing bowl. Stir well till combined.
Stir in the sugar, then sift in the flour, cocoa, baking powder and salt, if using.
Fold gently to combine and remove any lumps. Divide the batter equally among the ramekins.
Now make the topping. In a small bowl, combine the sugar and cocoa. Sprinkle evenly over the batter in all three ramekins. Stir together the hot water and whiskey, then pour into the ramekins, dividing the liquid equally among all three. Don't worry if it reaches the top of the ramekins, it will get absorbed.
Place the ramekins on a baking tray (line it with baking paper or a silicone mat first because the sauce might ooze onto the tray) and bake for 20 to 25 minutes, until a toothpick poked in the center of each pudding comes out clean, or only with a few moist crumbs. You'll see the sauce bubbling at the sides and if the puddings seem to have risen a bit, don't worry, they'll sink as they cool.
When the puddings are out of the oven, let them stand for a few minutes, then serve warm with whipped cream or vanilla ice cream! Best eaten fresh, but you can keep them in the fridge for 3 to 4 days, reheating as needed. Happy baking :)