To make the chocolate cupcakes:
Preheat oven to 350°F. Line two 12-count cupcake pans with 16 cupcake liners and set aside.
In a large mixing bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Whisk in the granulated sugar and brown sugar until well combined. Using a whisk or an electric mixer, mix in the oil, egg, vanilla extract, and buttermilk until just combined.
Add the instant espresso powder into the boiling water and mix until dissolved, then add to the mixing bowl. Mix with the rest of the ingredients until well combined, making sure not to over mix the batter. The batter will be thin, this is okay.
Evenly distribute the batter between all 16 cupcakes liners, making sure to only fill them a little over halfway full. Bake at 350°F for 18-20 minutes or until a wooden toothpick inserted into the cupcakes comes out clean. Remove from the oven and carefully remove the cupcakes from the pan. Transfer the cupcakes to a wire rack to cool.
To make the caramel frosting:
Add the butter to a saucepan and heat over medium heat until the butter is melted. Add in the brown sugar and heavy cream and stir until fully combined. Allow to cook for a few minutes until the sugar is dissolved and the mixture starts bubbling, reduce heat to low and continue cooking and stirring for 2 minutes. Remove from the heat and stir in the vanilla extract and salt until fully combined. Pour the caramel sauce into a mixing bowl and allow to cool for 15 minutes.
After 15 minutes, add in the powdered sugar and mix with a handheld mixer (or in the bowl of a stand mixer fitted with the whisk attachment) until fully combined. Pipe the frosting on the cooled cupcakes as desired, top with additional caramel sauce (or chocolate) and chopped pecans.