Make the Cookies:

Bring your eggs to room temperature by placing them in a glass of warm water for around 10 minutes.
In a small, microwavable bowl, melt the chocolate chips along with the oil and instant coffee. Heat in 30 second intervals, stirring each time, until chips are melted and smooth; set aside.
In a stand mixer fitted with the whisk attachment, add the eggs and sugar. Whisk on medium-high until thick, fluffy, and light in color, about 5 minutes.
Meanwhile, in a medium bowl, sift the cocoa powder, flour, baking powder, and salt. Whisk until combined and uniform in color; set aside.
Once the egg/sugar mixture has fluffed up and thickened, whisk in the vanilla. Then add the melted chocolate mixture and gently fold it into the egg/sugar mixture until totally combined. Add the dry ingredients and mix until just combined.
The dough will be like a very sticky, thick brownie batter. Allow it to sit at room temperature, uncovered, for 30 minutes. This allows the batter to stiffen up a bit so you can scoop the dough balls.
Preheat your oven to 350°F and line two baking sheets with parchment paper. Scoop cookies, eight at a time, 1 Tbsp in size onto one baking sheet. Gently shape and smooth each dough ball (optional). The dough balls should spread/flatten a bit once they’re scooped. If not, go ahead and use your fingers to gently flatten the tops of the dough balls.
Bake the cookies at 350°F for 5-7 minutes or until the centers no longer look wet. Let cool on the baking sheet for 2 minutes before carefully transferring to a cooling rack.
Meanwhile (or while the cookies are baking), use the room temperature baking sheet to prepare another batch of dough for the oven. Continue until all cookies are baked. Allow your cookies to cool completely before making the frosting.
Make the Frosting + Assemble:

In a medium bowl beat together the butter and peanut butter. Beat in the vanilla and powdered sugar. Finally, beat in the milk 1 tsp at a time until the frosting comes together and is thin enough to pipe but thick enough to hold its shape.
Add the frosting to a piping bag or large ziploc bag fitted with a large, circular piping tip. Pipe the frosting onto half of the cookies, holding the bag upright in the middle of the cookie and applying a steady pressure until the frosting nearly reaches the edge.
Sandwich the frosted cookies and plain cookies together, pressing gently until the frosting reaches the cookies’ edges.
Enjoy right away or store cookies in an airtight container in the refrigerator and eat them chilled like I do!