For the Chocolate Cookies
In a small mixing bowl, sift together flour, espresso powder, baking powder and salt. Set aside.
In heavy bottomed saucepan, melt the semi-sweet chocolate chips, unsweetened baking chocolate and butter over low heat. Stir until completely smooth. Take pan off the heat, allow to cool for 5-10 minutes.
In large mixing bowl, beat eggs, sugar and vanilla on medium-high heat, until pale yellow in color and fluffy. About 5-7 minutes. Beat in, on low, the cooled chocolate mixture, until completely incorporated. Beat in flour mixture, on low, for about 1 minute, until fully mixed in.
Let dough (it will look like a thick batter) rest for 5-10 minutes. (The dough will start to thicken up a bit and will look like soft frosting consistency.)
Scoop dough by tablespoon or using a #40 cookie scoop on to parchment-lined baking sheets.
Bake at 350 degrees F for 8-10 minutes, until edges are set. Cool on baking tray for 5-10 minutes; transfer to wire rack to cool completely.
For the Tiramisu Cream Filling
In measuring cup, stir together espresso powder and coffee, until completely dissolved. Set aside to cool.
In large mixing bowl beat butter until smooth and fluffy. Add 1 cup confectioners’ sugar and 1 tablespoon of coffee to butter, beat until smooth. Add in another cup confectioners’ sugar and 1 more tablespoon of coffee, beat until smooth. Add final cup confectioners’ sugar and last tablespoon of coffee, beat until mixture is smooth and fluffy. Scrape down the bowl and fold in the mascarpone cheese until completely incorporated.
To Assemble the Sandwich Cookies
Fill piping bag, fitted with a large round tip with the tiramisu cream. Lay out the cookies upside down in pairs. Fill one of the cookies with tiramisu cream, top with other cookie in pair. Repeat until all cookies are filled and topped.
Store in airtight container, in refrigerator. Serve cookies at room temperature. Enjoy!