Preheat your oven to 350°F/175°C and place 12 cupcake liners in your muffin tray. This recipe makes about 14 cupcakes, so you will need to make these in two batches.
In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, chocolate chips and salt. Set aside.
In a mug or cup, mix together the espresso powder and 2 tablespoon hot water.
In a large jug, whisk the eggs, espresso, oil, sour cream, vanilla, vinegar and two sugars until smooth
Pour the wet mixture into the flour, stirring until it is just about smooth - we don't want to over mix the batter!
Fill the cupcake liners ¾ of the way and bake for 18-20 minutes. A toothpick inserted should come out clean.
Allow the cupcakes to cool for 15 minutes in the tray, then take them out and place on a cooling rack. Bake the last two cupcakes.
Make Frosting
In a stand mixer fitted with the paddle attachment, beat the butter and confectioners' sugar together on low speed until well combined.
Increase the speed to medium-high and beat for a 2 minutes until it becomes very thick.
Stop the mixer and add the salt, vanilla, and espresso (mixed with the hot water!) into the bowl. Beat on medium-high speed for another 2 minutes.
Turn the mixer to your lowest speed and pour in the heavy cream. Beat until it becomes very creamy and spreadable.
I used a Wilton 1M piping tip to frost my cupcakes.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I have provided a conversion to US cups but please note that I haven't tested the recipe with this method. I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients (including the sour cream!) before you start baking. Butter: I use European style butter, like Kerry Gold, in my recipes. This will make your finished bake much creamier and richer.Salt: If you don't have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.Sour Cream: If you don't have sour cream you can substitute it for buttermilk. Cocoa Powder: I'm using dutch processed cocoa powder (not sure what you have? Check the ingredients. If it says 'acidity regulator' or mentions 'alkali', then it's dutch processed). If you want to use natural cocoa powder, then don't add the vinegar to the batter. Storage: Store the cupcakes in the fridge for up to 5 days. Let them sit at room temperature for 30 minutes before eating.