Hot Chocolate Brownie Cookie Sandwiches

Preheat the oven to 350°F / 175°C. Line a cookie sheet with parchment paper or a silicone baking mat.
In a small microwave safe bowl, melt together the chocolate chips and butter, stirring every 30 seconds until the mixture is smooth. Then, mix in the cocoa powder until smooth and set aside.
To another small mixing bowl, add in the egg and brown sugar. Vigorously whisk the egg and sugar together for 1-2 minutes, until the mixture is light and fluffy.
Add the melted chocolate mixture into the egg mixture, and mix gently until combined.
Add in the flour, baking powder, and salt. Use a rubber spatula to fold the ingredients just until no flour streaks remain. Note that the batter will be more liquidy like brownie batter, not as firm as cookie dough – this is normal!
Use two spoons to spread dollops of marshmallow fluff on top of the dough.
Use a small cookie scoop (1 ½ tbsp.) to dish out the cookies. Once all of the marshmallow fluff on top has been used, add on some more. Place the cookies spread apart on the baking tray to allow room for spreading.
Bake for 8-10 minutes, until the cookies have set on the edges.
Once the cookies come out of the oven, I recommend "scooting" them. This just means take a bowl, cup, or biscuit cutter that is slightly larger than the cookie, place it on top of the cookie, and swirl the bowl around to make the cookie a little more round.
While the cookies cool to room temperature, make the ganache.

Add the chocolate to a small mixing bowl. Heat the heavy whipping cream in a microwave until it starts to bubble up.
Pour the heavy cream over the chocolate and stir the mixture until the chocolate has all melted and the mixture is cohesive.
Place the ganache in the freezer for 10-20 minutes to allow it to firm up.
Once the ganache has firmed up and the cookies have cooled to room temperature, transfer the ganache to a piping bag fitted with your favorite piping tip.
Flip half of the cookies over, and place a dollop of marshmallow fluff in the center of the cookie. Use a culinary torch to toast the marshmallow (optional.) Pipe a ring of ganache around the outer circle, then top the cookie off with another cookie. Serve and enjoy!