Preheat the oven to 350 F and line two cupcake trays with 16 liners in total.
Combine hot water with espresso powder and mix until dissolved. Add cocoa powder and mix with a whisk or fork until all cocoa powder chunks have dissolved. Set aside to let cool before adding to the rest of the batter.
In a large bowl or mixing bowl, add cake flour, brown sugar, sugar, baking powder, baking soda, and salt. Mix until just combined.
In a separate bowl, combine whiskey, eggs, vanilla, and oil. Mix well until the egg yolks are thoroughly broken up. Add this mixture to the bowl with the dry ingredients and beat until just combined.
Scrape down the sides of the bowl and pour the cocoa mixture into the batter. Mix until just combined. Be careful not to over mix your batter!
Scoop about 3 Tbs of batter into each cupcake liner so that they are slightly over halfway full. (I like to use a ¼ measuring cup and just measure under slightly as ¼ cup is 4 Tbs.)
Bake for 15-20 minutes. My cupcakes are almost always done right at 17 minutes, but everyone’s oven is different so it is important to check them around the 15 minute mark. You can test if a cupcake is done by gently pushing down on the top of the cupcake. If it springs back, it’s ready. If it leaves a dent, it needs another couple minutes. You may also use a toothpick to test if the cupcakes are baked all the way through.
Let the cupcakes cool completely.
Using a fork or toothpick, poke some holes into each cupcake. Brush away any excess crumbs on top. Then, pour ½ tsp of whiskey onto each cupcake. Feel free to reduce it to ¼ tsp or omit it completely for less of a whiskey flavor.