Preheat the oven to 350°F.

In a medium mixing bowl, whisk to combine the flour, cornstarch, espresso powder, baking soda, and salt.

In the bowl of a stand mixer with the paddle attachment, combine the butter and sugar. Beat on medium speed for 3 minutes, until light and fluffy. Scrape down the sides of the bowl.

Add the egg and vanilla then mix on low speed for about 30 seconds, just until combined.

With the mixer on low speed, gradually add the flour mixture to the butter mixture and mix just until combined.

Scoop 1½ tablespoon-sized portions and roll each into a neat ball. Place the cookies about 2 inches apart on two baking sheets.

Bake for 9 to 10 minutes or until the edges are lightly golden. Let them cool on the baking sheets for about 5 minutes before transferring to a rack.

In a large mixing bowl or a stand mixer with the whisk attachment, beat the mascarpone, cream cheese, powdered sugar, vanilla, and salt on medium speed until creamy.

With the mixer running, slowly drizzle in the cold cream until the mixture is creamy. Increase the speed to medium and beat until fluffy, stiff peaks form.

Transfer the icing to a piping bag and pipe the icing on the top of each cookie.

Sprinkle cocoa powder over top. Serve the cookies immediately or store in a container in the refrigerator for up to 3 days.