Preheat the oven to 350°F/177°C. Line a 12-cup muffin pan with cupcake liners. This recipe makes 12 to 15 cupcakes, so have a second pan and a few more liners handy. Set aside.
Using a whisk, mix together the flour, cocoa powder, espresso powder (if using), baking powder, baking soda, and salt together in a large mixing bowl until well combined. Set aside.
In a medium mixing bowl, whisk the eggs, granulated sugar, brown sugar, oil, butter, vanilla, and buttermilk together until completely combined and smooth.
Pour the wet ingredients into the dry ingredients and gently mix until just combined being careful not to over mix. The batter will be thin.
Fill the liners two-thirds full with the batter. Bake for 18-21 minutes, or until a cake tester comes out clean. Allow to cool completely before frosting.
For the frosting:
Heat the cream, in a small saucepan or in the microwave until it's hot and starts to bubble.
Place chocolate in a medium bowl and pour over the hot cream. Let stand for 5 minutes. Add the salt and whisk until the chocolate has melted completely and the mixture is smooth.
Cover with plastic wrap and set aside to cool and thicken. It will fully cool within 2 hours at room temperature. Refrigerating will expedite things, but the frosting may not set evenly. Stir it a few times as it sets in the refrigerator so it remains even and smooth.
Frost cooled cupcakes and cover in chocolate curls.
I suggest using chocolate that is no more than 60% Cocoa solids as higher percentages chocolates are much harder to melt and can cause your ganache to break or cease.
When ingredients are at different temperatures, they don’t combine well. Bringing ingredients to the same temperature helps them to mix together better.
Only Mix your batter until the wet and dry ingredients are just combined. Overmixing will result in a tough, dense cupcake.
Use good quality, grease-proof liners to avoid your cupcakes sticking to the liner.
Follow the recipe instructions. Over or underfilling can lead to disaster. When in doubt, fill the liners 2/3 of the way full.
Allow your chocolate cupcakes to cool completely before frosting – This may sound like a no-brainer, but if you’re a beginner, you may not know that trying to frost a warm cupcake will cause the frosting to melt and slip right off. Be patient and wait until they are completely cool.