Preheat your oven to 350°F/175°C and place 7 cupcake liners in your cupcake pan.
In a medium bowl, whisk together the flour, sugar, light brown sugar, cocoa powder, baking powder, baking soda and salt. Set aside.
½ cup + 1 tablespoon all-purpose flour, ¼ cup granulated sugar, ¼ cup light brown sugar, ¼ cup natural cocoa powder, ¼ teaspoon baking powder, ½ teaspoon baking soda, ¼ teaspoon kosher salt
In a jug, whisk the egg, oil, sour cream, and vanilla until smooth.
1 large egg, 2 tablespoons + 2 teaspoons vegetable oil, ½ teaspoon vanilla extract, ¼ cup sour cream
Pour the wet mixture into the flour, stirring until it is just about smooth - we don't want to over-mix the batter! Then pour in the hot water and mix until smooth.
¼ cup hot water
Fill the cupcake liners so they're just under ¾ full 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.
Chocolate Frosting
Melt your chocolate in a microwave, stirring every 10-15 seconds so it doesn't burn.
1.5 oz semisweet chocolate
In your stand mixer with the paddle attachment, or in a bowl with a handheld mixer, beat the butter and confectioners' sugar on low speed until well combined
¼ cup unsalted butter, ½ cup confectioners’ sugar
Turn the speed to high for 2-3 minutes until light and fluffy.
Add in your cocoa powder and beat on low, then increase the speed to medium for 1-2 minutes.
¼ cup Dutch-processed cocoa powder
Add your sour cream, melted chocolate and salt and mix once more.
pinch kosher salt, 2 tablespoons sour cream
Frost the cupcakes and enjoy! This is enough frosting to ice your cupcakes, but if you want a large amount of frosting for each cupcake I recommend doubling the frosting recipe!
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.
Ingredients: I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients before you start baking.
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. Please note, I'm using Diamond Crystal kosher salt and not Morton salt which is too salty!
Cocoa Powder: I'm using natural unsweetened cocoa powder (not sure what you have? Check the ingredients. If it says 'acidity regulator' or mentions 'alkali', then it's dutch processed). You can use Dutch-processed or natural for the frosting!
Storage: You can store the cupcakes in the fridge for 3-4 days. I recommend letting it come to room temperature before enjoying!