Preheat the oven to 350°F / 175°C. Butter and line an 8x4" loaf pan with parchment paper.
In a medium-sized microwave safe mixing bowl, melt together the butter and chocolate chips in 30 second intervals, stirring in between each interval.
Once the mixture is melted and smooth, whisk in the cocoa powder, sugar, and instant espresso.
Add in the egg and egg yolk and whisk the mixture vigorously for 1-2 minutes, until well combined.
Add in the flour and salt. Use a rubber spatula to lightly fold the flour into the mixture just until the last streak of flour disappears.
Pour the brownie batter into the loaf pan and smooth it out into an even layer. Bake for 25-30 minutes, or until the edges are set and the center only slightly wobbles. (You can also check for doneness with a thermometer: it should read at least 180F/82C)
Mascarpone Whipped Cream
While the brownies are cooling, make the mascarpone whipped cream.
In a medium sized mixing bowl with a hand or stand mixer, beat together the mascarpone, sugar, and vanilla just until the mixture is cohesive.
Slowly beat in the heavy whipping cream. Once all of the heavy cream has been added, beat the mixture until soft peaks form.
Cover the whipped cream and place it in the fridge until you're ready to assemble the brownies. If you're using espresso for the ladyfinger soak, brew it at this point as well and set it in the fridge to cool.
Ladyfinger Soak
Once the brownies have fully cooled to room temperature, it's time to assemble them.
In a small shallow bowl, combine the cooled espresso and coffee liquor (optional.)
Dip the ladyfingers into the cofee mixture on both sides, then place them on top of the brownies.
Top the ladyfingers with the mascarpone whipped cream. If you want to pipe a design on top of the brownies, I recommend spreading a thin layer of the mascarpone cream over the ladyfingers before using the rest of the mascarpone cream to pipe a design on top.
Cover the brownies and place them in the fridge to chill and set up for at least 1 hour.
Dust the top of the brownies with cocoa powder, then slice, serve, and enjoy!