Preheat the oven to 350 F. Line 2 muffin tins with 16 cupcake liners in total.
In a microwave-safe bowl, microwave the Guinness and water together for about 45 seconds - 1 minute until it is hot enough to dissolve the espresso powder.
Once your Guinness and water mixture is hot enough, add your espresso powder and cocoa powder. Mix with a fork or whisk until the cocoa powder and espresso powder have dissolved and you're left with a brownie batter- like mixture. Set aside to cool.
In your large mixing bowl, beat together the brown sugar, granulated sugar, and oil together for about 1-2 minutes until fully combined.
In a separate small bowl, add the eggs and vanilla. Use a fork to lightly beat the mixture until both egg yolks are broken up.
Add the eggs and vanilla into your butter and sugar mixture in two parts, beating each one thoroughly until fully incorporated.
In a separate medium bowl, add your cake flour, baking soda, baking powder, and salt. Mix until just combined.
Add your flour mixture to the large mixing bowl and beat on low-medium speed. When the flour starts to mix in, slowly stream in the chocolate and Guinness mixture. Mix until just combined. Your batter will be pretty runny.
Use a 1/4 measuring cup to scoop your batter into each cupcake liner, filling them about 2/3rds of the way full.
Bake at 350 F for 15-22 minutes until the top springs back when gently poked or until a toothpick comes out clean.
Once the cupcakes have cooled, use a fork to poke holes in each cupcake. Pierce each cupcake three times. Then, pour 1/4 teaspoon of Guinness on top of each cupcake. (Skip this step if you don't enjoy the taste of Guinness)