1. Preheat oven to 350 F. Line large baking sheet with parchment paper and set aside. 
2. In a medium bowl whisk together flour, baking soda, cornstarch, salt and instant espresso powder. Set aside.
3. In a mixer bowl, add the butter and sugars. Beat on medium speed for 3 minutes or until combined.
4. Add the egg, egg yolk and vanilla extract. Beat on medium/high speed for 3-4 minutes or until the mixture is combined and fluffy. 
5. Add the flour mixture. Beat until flour has incorporated into the dough. 
6. Using a cookie scoop, scoop cookie dough and place about 2 inches apart on prepared parchment paper. 
7. Bake for 10 minutes or until cookies are lightly golden brown around the edges. Do not over bake!
8. Cool completely before frosting.

Mascarpone frosting

1. Beat heavy whipping cream until stiff peaks form then set aside. 
2. Beat mascarpone cheese, powdered sugar, vanilla extract and instant espresso powder until combined. (Taste the frosting, and add more coffee/powdered sugar if needed)
3. Fold in heavy whipping cream until combined. 
4. Pipe frosting onto cookies then sprinkle with cocoa powder.