The show stopper of this recipe is the sriracha chocolate truffle. You get the bold flavor of sriracha, which lends a touch of savory richness to this cake, and then you get a nice slow burn as you continue eating. Definitely a must for anyone who likes heat and chocolate! —melomel
Work on the Sriracha Chocolate Truffle Filling first so it has time to chill (at least 30 minutes).
Measure the chocolate into a heat-safe bowl.
Bring the heavy cream and butter to a boil. Take off the heat and pour over the chocolate, then add the sriracha.
Stir until the chocolate melts and isn't lumpy. Set aside to cool for 10 minutes at room temperature, then chill in the fridge for about 30 minutes (it shouldn't be rock hard, but it also shouldn't be soupy...look for the consistency of buttercream).
Heat the oven to 350 degrees Fahrenheit and position the racks toward the middle. Line cupcake pans with cupcake papers.
For the cupcakes, combine flour, baking soda, salt and sugar, whisking to blend; set aside.
In a heavy-bottomed, medium pan, melt the butter on medium-high heat. Once melted, add the coffee, instant espresso and whisk together. Add the cocoa—gradually—whisking to combine. The mixture should come to a simmer, but not a boil. You want it to thicken.
Once thickened, cool the cocoa mixture for about 15-20 minutes at room temperature, whisking occasionally to release more heat
In your stand mixer, whip together the eggs and milk.
Once the cocoa mixture has cooled some, slowly add a little bit of it to temper the eggs, whisking constantly. Continue to slowly add the remaining mixture, whisking to combine. If you don't want to whisk by hand, and have a stand mixer, then set the speed on low and slowly pour the cocoa mixture in.
Add the dry ingredients in 3-4 stages, mixing well to combine. Add the vanilla extract and chili flavoring (if using) and mix well.
Divide batter evenly among lined cups, filling each about halfway full. Bake for about 18-22 minutes. When done, transfer tins to wire racks to cool 10 minutes; turn out cupcakes onto racks and let cool completely.
Core the cupcakes, fill a piping bag with the filling and pipe into each cupcake.
To make the buttercream, beat the butter until light and fluffy.
Add 1 cup of sugar, beating until combined. Add the cocoa powder and vanilla.
Finally, add the remaining sugar gradually and heavy cream (as needed) and whip until light and fluffy.
Place the buttercream in a piping bag and pipe the frosting onto your filled cupcakes.