Step 1

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.

Step 2

Cook over medium heat, stirring constantly, until the mixture thickens and can coat the back of a spoon, about 10 minutes.

Step 3

Add the chopped chocolate and continue to cook, stirring often, for about 4 minutes, or until the pudding is smooth and very thick.

Step 4

Remove from heat and stir in the vanilla. Pass the mixture through a fine-mesh strainer into a large serving bowl.

Step 5

Place 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.

Step 6

Preheat oven to 350 degrees (F). Line (12-cup muffin tins with cupcake liners. Spray lightly with non-stick baking spray, and set aside.

Step 7

In a large bowl, sift together the flour, cocoa powder, baking soda, baking powder, and salt. Set aside until needed.

Step 8

Combine 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.

Step 9

In a large bowl, combine both sugars, eggs, egg yolk, and vanilla and beat until smooth and well combined.

Step 10

Gradually add in the melted chocolate mixture, adding a little bit at a time and whisking constantly.

Step 11

Gently 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.

Step 12

Pour in the hot coffee (or water) and let it sit for 30 seconds, then fold it into the batter until combined.

Step 13

Fill 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.

Step 14

Allow cupcakes to cool completely before frosting!

Step 15

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.

Step 16

In 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.

Step 17

On 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.

Step 18

Decrease 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.

Step 19

Once 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).

Step 20

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!

Step 21

Scrape the chilled pudding into a large piping bag fitted with a medium piping tip, like this one.

Step 22

Pipe the filling into the middle of each cupcake cavity, filling it all the way to the top.

Step 23

Next, 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.

Step 24

Crumble up the cupcake scraps into fine crumbs and sprinkle a generous amount on top of each cupcake.

Step 25

Serve 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.