For the cake batter: Preheat the oven to 350 degrees F. Line a standard muffin pan or cupcake pan with 12 cupcake liners.
Mix the coffee extract into the brewed coffee. Set aside and allow to cool slightly.
In a bowl of a stand mixer, sift together the flour, granulated sugar, brown sugar, cocoa, baking powder, baking soda and salt and mix to combine. Add the butter, vanilla and eggs and beat on medium speed until combined. Add half of the coffee and beat for 20 seconds. Scrape the sides of the bowl and add the remaining coffee. Beat for another 20 seconds until the batter is smooth.
Divide the batter among the cupcake liners, filling them three-quarter full. Bake until a tester inserted into the centers comes out clean, about 18 minutes. Set the pan on a rack to cool.
For the ganache: In a medium saucepan, bring the cream, corn syrup and granulated sugar to a boil over medium-low heat, whisking until the sugar is dissolved. Remove the pan from the heat and add the chocolate, whisking until the chocolate is melted. Add the coffee extract and whisk until smooth. Add the butter and whisk until smooth. Transfer the ganache to a bowl to cool.
For the salted caramel coffee frosting: If using the espresso powder, mix the espresso powder and the vanilla together in a small bowl until dissolved and set aside.
Using a stand mixer with a whisk attachment, whip the butter on medium-high speed until creamy. Add the caramel and beat until combined. Reduce the speed to low, add half of the confectioners' sugar and mix until incorporated. Add the rest of the confectioners' sugar and mix until combined. Add the coffee extract and vanilla (or the espresso powder and vanilla mixture) and continue to mix at medium-high speed until completely incorporated, scraping the sides as necessary. Whip the frosting until fluffy. If necessary, use 1 to 2 tablespoons milk to loosen the frosting.
To assemble: Cut a small and shallow hole in each cupcake and fill with the ganache. Frost the cupcakes with the salted caramel coffee frosting and sprinkle with a few granules of fleur de sel.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.