For the Ganache Filling:

1. Chop the chocolate. Then scald the heavy cream and pour it over the chocolate. Stir until smooth and add the Kahlua, then set aside or refrigerate to solidify.

For the Cupcakes:

1. In a large bowl, melt together the chocolate, butter and water (I used the microwave, but double boiler works too). When the water is steamy, remove from heat and whisk to combine. Whisk in the espresso powder and cocoa powder until smooth. Set aside to cool slightly.
2. Preheat the oven to 350F and line two muffin pans (for 24 muffins) with cupcake liners.
3. In a medium bowl, mix together the flour, granulated sugar, brown sugar, salt, and baking soda.
4. In the cooled water/chocolate mixture, whisk in the yogurt, eggs and yolks one at a time, and vanilla extract. When it’s all incorporated, slowly fold in the flour mixture until completely combined, but do not over-mix.
5. Scoop the batter into the prepared cupcake pans. Scoop out about a tablespoon of hardened ganache and plop it into the center of each cupcake. Throw ’em in the oven for 18-20 minutes, or until a toothpick in their side comes out clean. Meanwhile, work on your buttercream.

For the Buttercream:

1. Mix the espresso powder into the brewed espresso, and set aside or refrigerate to cool completely.
2. In the bowl of an electric stand mixer or another heat proof bowl, whisk together the egg whites, sugar, and pinch of salt. Place the bowl over a pot of simmering water, and stir occasionally as the egg whites heat up and the sugar dissolves. After about 7-9 minutes, the whites should be hot. Remove from heat and get ready to beat it.
3. Beat on medium speed to thicken the egg whites, then bump it up to high until stiff peaks form and they’ve cooled somewhat, about 10 minutes.
4. Slowly add the softened butter, a tablespoon at a time. Not only is this how your egg whites become buttercream, but it also serves to slowly lower the temperature of the egg whites. Take your time to add the butter, it should take at least 15 minutes.
5. With the mixer on low, add the cooled brewed espresso slowly. Continue to beat on medium-high speed until it all comes together. It may curdle and come apart at first, but have faith. If you’re having issues, check out my tips on buttercream here.
6. Once the cupcakes are done baking and have cooled completely, use a piping bag and a 2D piping tip to frost the cupcakes. Leftover buttercream can be refrigerated or frozen, and can be brought back to life by bringing it back to room temperature before beating it together. Cupcakes will last for a few days in the fridge, or even at room temp if you’ve got a cool-ish kitchen.