Creating Tiramisu Sandwich Cookies is a delightful process. Follow these simple steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
2. Mix Dry Ingredients: In a bowl, whisk together the flour, cocoa powder, baking powder, and salt.
3. Cream Butter and Sugar: In another bowl, cream together the softened butter and granulated sugar until light and fluffy.
4. Add Egg and Extracts: Beat in the egg, vanilla extract, and brewed espresso until well combined.
5. Combine Mixtures: Gradually add the dry ingredients to the wet mixture, stirring until just combined.
6. Scoop Dough: Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.
7. Bake: Bake in the preheated oven for 12-15 minutes, or until the edges are set. The cookies may look soft; they will firm up as they cool.
8. Cool the Cookies: Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
9. Prepare the Filling: In a mixing bowl, whip the heavy cream until soft peaks form. In another bowl, mix the mascarpone cheese, powdered sugar, vanilla extract, and optional espresso until smooth. Gently fold in the whipped cream until combined.
10. Assemble the Cookies: Once the cookies are completely cool, spread a generous amount of the mascarpone filling on the flat side of one cookie, then top it with another cookie to create a sandwich.
11. Chill: Place the assembled cookies in the refrigerator for at least 30 minutes to allow the flavors to meld.