First, make and bake your espresso chip cookie bar base. Melt your butter and stir in your espresso powder.
Add in your light brown and granulated sugars and combine using a spatula.
Add in your egg, egg yolk and vanilla extract and continue to mix.
Add in your flour, baking soda and salt. Fold your dry ingredients into your butter mixture until a shaggy dough forms.
Add in your chocolate chips and chopped chocolate and continue mixing.
Into a parchment lined 9x9 inch square pan, add your espresso chip dough and spread across your pan until even. Place into the fridge to chill uncovered for 2 hours.
Preheat your oven to 350 degrees and bake your cookie bars for 24 to 26 minutes.
Allow your cookie bars to completely chill.
In a bowl, combine your cold mascarpone with powdered sugar and vanilla extract.
In a separate bowl, whip your heavy cream to stiff peaks.
Fold your whipped cream into your mascarpone mixture until completely combined.
Spread or pipe your mascarpone topping onto your chilled espresso chip cookie bars.
Sift cocoa powder on the top of your mascarpone topping.
Chill your bars for an hour or two before enjoying.
