Preheat your oven to 350°F/175°C and place 12 cupcake liners in your cupcake pan.
In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt. Set aside.
¾ cup all purpose flour, ½ cup cocoa powder, ¾ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon kosher salt
In a mug or small cup, mix together the espresso powder and 2 tablespoon hot water until the espresso powdered has dissolved.
1 teaspoon espresso powder, 2 tablespoon hot water
In a large jug, whisk the eggs, espresso, oil, sour cream, vanilla, vinegar, light brown sugar and white sugar until smooth
2 large eggs, ½ cup light brown sugar, ¼ cup vegetable oil, 1 teaspoon vanilla extract, ½ cup sour cream, 2 teaspoon white vinegar, ½ cup sugar
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.
Make Salted Caramel
Take a small saucepan and place it on your stove over medium-low heat. Add the sugar ¼ cup at a time, letting the sugar dissolve completely until you add the next ¼ cup.
1 cup white sugar
Stir over the heat until all of the sugar has dissolved and it has turned a dark amber color. Turn the stove off.
Add the butter one tablespoon at a time, stirring after each addition. Careful as it may sputter!
6 tablespoons unsalted butter
Pour in the heavy cream, vanilla extract and salt. Stir until combined. Pour the caramel (carefully!) into a large jar and let cool. It will become very thick.
4 tablespoons heavy cream, ½ teaspoon kosher salt, ½ teaspoon vanilla extract
Make Frosting
In a stand mixer fitted with the paddle attachment, beat the butter and confectioners' sugar together on low speed until well combined.
Turn the mixer to your lowest speed and pour in the heavy cream. Beat until it becomes very creamy and spreadable.
1 tablespoon heavy cream
Assembly
Use a large piping tip to core out each cupcake. You may need to use a knife or small spatula to dig out some of the cake in case the tip didn't go down far enough. You want to make sure you have some space in each cupcake so they get filled!
Put the remaining caramel in a piping bag, or you can just use a spoon if you prefer. Pipe caramel into each cupcake.
Fill another piping bag with the caramel frosting and frost each cupcake. I like using the Wilton 1M or 4B tip!
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 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. Salted Caramel: this salted caramel is quite thick. Prefer a thinner caramel? Use 5 tablespoons of butter instead of 6 and increase the heavy cream to 8 tablespoons. If you make the caramel in advance and it has hardened, you can warm it up in the microwave. Storage: Store the cupcakes in the fridge for up to 5 days. Let them sit at room temperature for 30 minutes before eating.