6 Tbsp (85 g) butter, room temperature
1/2 c (106 g) sugar
5 Tbsp (43 g) brown sugar
1 1/2 tsp salt
3/8 tsp baking powder
1/4 tsp baking soda
1 tsp espresso powder
1 1/2 tsp vanilla extract
2 egg yolks
3/4 c + 1 Tbsp (113 g) flour, sifted
1 c (85 g) cocoa powder, sifted
In a large bowl, cream together the butter, white sugar, brown sugar, salt, baking powder, baking soda, espresso powder and vanilla until thoroughly mixed. With the mixer still running, add in the egg yolks one at a time, scraping the sides of the bowl with a rubber spatula well after each addition.
After the yolks have all been incorporated, add the flour and cocoa. Mix on low speed until uniform and stiff. Scrape the sides of the bowl using a rubber spatula and knead a few times to form a smooth ball. Flatten into a disc.
At this point, the dough may be rolled right away or wrapped in plastic wrap and refrigerated for up to a week.
If you choose to refrigerate the dough, make sure you allow it to soften at room temp before rolling.
Otherwise, preheat oven to 350F. Dust the counter with cocoa powder (better than flour because it ensures they will not have a white powdery finish) and roll the dough to a thickness of 1/8". When the dough has been rolled, loosen it from the counter with a spatula to prevent sticking.
Using a 2" round cutter, cut out as many cookies as you can. Use a metal spatula to place them on an ungreased baking sheet. The cookies won't spread during baking, so you can place them quite close to one another. Set the baking sheets aside while you repeat the process with the scraps.
After cutting rounds from the re-rolled scraps, place remaining scraps into a mixing bowl. Add 1 tsp of hot water and coffee and mix thoroughly. Continue adding more hot water or coffee, a teaspoon at a time, until you reach a piping consistency.
Transfer the softened dough to a piping bag fitted with a very small tip and pipe your preferred decoration onto the cut rounds. Stella recommends a tight cornelli, which I thought worked quite well, but you can do whatever you like!
Bake the bedecked cookies for about 12 minutes, or until firm to the touch. Do not wait for them to brown because browning chocolate cookies = burning chocolate cookies! Once the cookies have baked, set the baking sheet on a rack and cool thoroughly.
4 Tbsp (58 g) shortening or unsalted butter at room temperature
1 c - 2 Tbsp (142 g) powdered sugar, sifted
1 tsp vanilla
1/8 tsp salt
Cream together the shortening/butter, powdered sugar, vanilla, and salt until very light and fluffy, about five minutes. Use a rubber spatula to scrape the sides of the bowl then beat again briefly to incorporate.
Transfer the filling to a pastry bag fitted with a small- to medium-sized round tip.
Flip half the cookies upside down and pipe a spiral of frosting onto the upside down cookies. Top with another cookie and press gently to seal. Transfer prepared cookies to a sealed container and refrigerate for a few hours to set the frosting and bond the wafers.