Follow these simple steps to make your Tiramisu Sandwich Cookies:

1. Preheat Oven: Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
2. Mix Dry Ingredients: In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt. Set aside.
3. Cream Butter and Sugar: In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.
4. Add Egg and Vanilla: Beat in the egg and vanilla extract until well combined.
5. Incorporate Coffee: Add the cooled brewed coffee to the mixture and stir until combined.
6. Combine Mixtures: Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
7. Scoop Dough: Use a cookie scoop or tablespoon to drop rounded dough onto the prepared baking sheet, spacing them about 2 inches apart.
8. Bake: Bake in the preheated oven for 15-20 minutes, or until the cookies are set and slightly firm to the touch.
9. Cool: Remove from the oven and allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to wire racks to cool completely.
10. Prepare the Filling: In a separate bowl, combine the mascarpone cheese, powdered sugar, vanilla extract, and cooled coffee. Mix until smooth and creamy.
11. Assemble Cookies: Once the cookies have cooled, spread a generous amount of filling on the flat side of one cookie, then top with another cookie to create a sandwich.
12. Dust with Cocoa: If desired, dust the assembled cookies with cocoa powder for that authentic tiramisu finish.