1. Preheat the oven to 350°F (176°C) and line a cupcake pan with cupcake liners.
2. Beat the butter and sugar until light in color and fluffy, about 3-4 minutes.
3. Add eggs one at a time, beating just until blended.
4. Add vanilla, 6 tablespoons of Guinness and cocoa powder to another bowl and whisk until smooth. Mixture will be thick.
5. Add chocolate mixture to batter and mix until combined. Scrape down the sides of the bowl as needed to make sure everything is well combined.
6. Combine flour, baking soda and salt in a separate bowl.
7. Alternate adding the flour mixture and the remaining 6 tablespoons of Guinness to the batter. Begin by adding half of the dry mix, then mix well. Add the Guinness and mix well, scraping down the sides as needed. Add the remaining flour mixture and mix until smooth.
8. Fill cupcake liners about 3/4 way. Bake for 15-17 minutes, or until a toothpick inserted comes out with a few crumbs.
9. Allow cupcakes to cool about 2-3 minutes, then remove to a cooling rack to finish cooling.
10. When the cupcakes are cooled, make the frosting. Beat the butter in a large mixer bowl and mix until smooth.
11. Add the melted chocolate and mix until well combined.
12. Add the cocoa powder and mix until well combined.
13. Add about half of powdered sugar and 2 tablespoons of Guinness or heavy cream and mix until well combined.
14. Add remaining powdered sugar and salt and mix until smooth.
15. Add remaining Guinness or heavy cream as needed to get the right consistency of frosting.
16. To make the chocolate ganache, put the chocolate chips in a heat-proof bowl.
17. Combine the Guinness and heavy whipping cream in a microwave safe bowl or measuring cup and heat in the microwave until it just begins to boil.
18. Pour the hot cream over the chocolate chips and whisk until smooth.
19. Cut out the centers of the cupcakes. You can use a cupcake corer or a knife.
20. Fill the centers of the cupcakes with chocolate ganache.
21. Pipe the frosting onto the cupcakes, then add some sprinkles. I used Ateco tip 844.
22. Refrigerate cupcakes until ready to serve. Serve at room temperature. Cupcakes are best for 2-3 days.