Preheat your oven to 350°F (175°C). Line a muffin tin with cupcake liners and set aside.
In a large mixing bowl, whisk together the eggs, buttermilk, Greek yogurt, canola oil, and vanilla extract until well combined.
In another bowl, sift together the all-purpose flour, granulated sugar, cocoa powder, baking soda, baking powder, and kosher salt.
Gradually add the dry ingredients to the wet ingredients while mixing. Slowly pour in the hot black coffee, mixing until just combined. If using mini chocolate chips, fold them in at this stage.
Using a scoop or spoon, fill each cupcake liner about two-thirds full with the batter.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
Once baked, allow the cupcakes to cool in the tin for 5 minutes, then transfer them to a wire cooling rack to cool completely.
In a large mixing bowl, beat the softened salted butter until creamy. Gradually add the powdered sugar and cocoa powder, mixing until smooth. Add the vanilla extract and whipping cream.
Once the cupcakes are completely cool, frost them generously with the fudgy buttercream using a spatula or a piping bag.
Decorate with additional chocolate chips or sprinkles if desired. Serve and enjoy!
