Preheat oven to 350 degrees. Line baking sheet with parchment paper or nonstick mat; set aside.
In a bowl, whisk together the flour, instant espresso powder, baking powder, cinnamon, nutmeg, and salt until well combined; set aside.
In a large bowl, use a handheld mixer to beat together the ¾ cup of butter and sugar until light and fluffy; about 2 minutes. Add in the eggs and 2 tablespoons of Kahlua and mix until combined. Pour in the dry ingredients and mix until just combined.
Use a cookie scoop to measure out equal-sized balls of dough and place on cookie sheet leaving about 2 inches between each cookie (you should be able to get a dozen cookies per baking sheet). Bake in preheated oven for about 12 minutes. Let cool on cooling rack completely before frosting.
To make the frosting, use a handheld mixer to mix together the mascarpone and butter until fluffy; about a minute. Then, add in the 1 teaspoon of Kahlua and mix. With the mixer on low, add in the powdered sugar until frosting is well combined. Spread about a tablespoon of the frosting over each cooled cookie and dust with cocoa powder before serving.
Video
Notes
Use room temperature ingredients so that the everything mixes together evenly.
If you don't have Kahlua, you can substitute another coffee liqueur or use other common tiramisu liquors such as rum, cognac, or marsala wine.
Roll the dough into balls before baking to have more uniform cookies.
Make sure the cookies are completely cooled before adding the frosting.
Tiramisu Cookies can be made ahead but must be chilled because of the frosting. Refrigerate in an airtight container for up to a week.
You may have leftover mascarpone frosting. It's great to use to top cupcakes or stir into your coffee!