The Best Brooklyn Blackout Cupcakes

Steps

1. 1For the Chocolate Pudding: In a small, heavy bottomed saucepan, combine the cornstarch and both sugars. Gradually pour in the milk, adding it a little bit at a time, and whisking well to ensure no lumps form in the mixture.
2. 2Cook over medium heat, stirring constantly, until the mixture thickens and can coat the back of a spoon, about 10 minutes.
3. 3Add the chopped chocolate and continue to cook, stirring often, for about 4 minutes, or until the pudding is smooth and very thick.
4. 4Remove from heat and stir in the vanilla. Pass the mixture through a fine-mesh strainer into a large serving bowl.
5. 5Place plastic wrap on top of the pudding and smooth it gently against the surface. Refrigerate for at least 2 hours, or up to 3 days.
6. 6For the Blackout Chocolate Cupcakes: Preheat oven to 350 degrees (F). Line (2) 12-cup muffin tins with cupcake liners. Spray lightly with non-stick baking spray, and set aside.
7. 7In a large bowl, sift together the flour, cocoa powder, baking soda, baking powder, and salt. Set aside until needed.
8. 8Combine the oil, butter, and chocolate together in a large bowl. Heat in the microwave, in 30 second increments, stirring between increments each time, until the butter and chocolate are completely melted. Stir in the espresso powder. Set aside and cool while you assemble the other ingredients.
9. 9In a large bowl, combine both sugars, eggs, egg yolk, and vanilla and beat until smooth and well combined.
10. 10Gradually add in the melted chocolate mixture, adding a little bit at a time and whisking constantly.
11. 11Gently fold in the flour in 3 additions, alternating with the sour cream, beginning and ending with the flour. Mix gently and stop when you can still see the lightest trail of dry ingredients.
12. 12Pour in the hot coffee (or water) and let it sit for 30 seconds, then fold it into the batter until combined.
13. 13Fill each cupcake liner so that they're 2/3 full with batter. Bake, one tray at a time, for 16 to 18 minutes, or until the cupcakes have puffed up and a toothpick (or cake tester) inserted in the middle of a cupcake comes out clean, or with a few moist crumbs attached.
14. 14Allow cupcakes to cool completely before frosting!
15. 15For the Fudgy Chocolate Frosting: Place both chocolates in a microwave-safe bowl. Heat in the microwave, on low power, in 30 second increments, stirring between each increment, until the chocolate is completely smooth and melted. You may also do this in a double-boiler. Set aside and cool until tepid.
16. 16In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl using a handheld electric mixer, beat the butter until completely smooth.
17. 17On low speed, add in the confectioners' sugar, a little bit at a time, beating until each addition has been completely incorporated into the butter before adding more. Once all of the sugar has been added, increase speed to medium-high and beat for 3 minutes.
18. 18Decrease the speed back to low and beat in the vanilla extract. Then slowly pour in the cooled melted chocolate and continue mixing until well combined, tuning the mixer off and scraping down the sides and bottom of the bowl as needed.
19. 19Once all of the chocolate has been added, increase the speed back to medium-high and beat for 2 minutes. Set aside for 30 minutes to firm up, or up to 3 hours. Do not refrigerate (the chocolate will seize and render the frosting impossible to spread).
20. 20Assembly: Using a paring knife, cut out a 1/2" inch cone shaped hole in the middle of each cooled cupcake. The hole should stop about 1/4" from the bottom of the cupcake, to avoid breaking the base. Set all of the cupcake scraps aside!
21. 21Scrape the chilled pudding into a large piping bag fitted with a medium piping tip, like this one.
22. 22Pipe the filling into the middle of each cupcake cavity, filling it all the way to the top.
23. 23Next, scrape your fudgy chocolate frosting into a piping bag fitted with an open star piping tip, like this one. Pipe the frosting on top of each cupcake, making sure the pudding is completely covered.
24. 24Crumble up the cupcake scraps into fine crumbs and sprinkle a generous amount on top of each cupcake.
25. 25Serve at once, or store in the fridge until needed. Cupcakes are best served the day they are made, but will keep, stored in the fridge, for 2 days.