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 (or a large bowl using a handheld mixer), 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 (about 30g) and roll each into a neat ball. Place the cookies about 2 inches apart on two parchment or silicone-lined baking sheets.

Bake for 9 to 10 minutes or until the edges are lightly golden and the cookies are puffed and dry on top. Let them cool on the baking sheets for about 5 minutes before transferring to a cooling rack to cool completely.

In a large mixing bowl or the bowl of a stand mixer fitted with the whisk attachment, beat the mascarpone, cream cheese, confectioners’ sugar, vanilla, and salt on medium speed until creamy and well combined, about 1 minute.

With the mixer running on medium-low speed, slowly drizzle in the cream. Once added the mixture is creamy, stop and scrape down the bowl. Increase the speed to medium and beat until fluffy, stiff peaks form, 1 to 2 minutes. Mix in the Kahlua, if using.

Transfer the icing to a piping bag and cut a ½-inch wide opening from the tip. Pipe the icing on the top of each cookies starting in the center of the cookie and piping around in a concentric-circle-like shape.

Place a few tablespoons of cocoa powder in a sifter or fine mesh sieve and sprinkle over top. Serve the cookies immediately, or store in a single layer in an air-tight container in the refrigerator for up to 3 days, though they have the best texture if eaten within the first 24 hours.