For Cookies

1. Preheat oven to 350 degrees
2. Line two baking sheets with parchment paper. Set aside.
3. Over a double boiler, melt unsweetened chocolate, bittersweet chocolate and butter. Stir frequently until the chocolate and butter are completely melted and smooth. Remove the bowl from heat and set aside to cool slightly, about 10-15 minutes.
4. Meanwhile, in a separate mixing bowl, whisk together flour, baking powder, cinnamon, cayenne pepper and salt. Set aside.
5. In the bowl of a stand mixer fitted with the paddle attachment, mix sugar, eggs and vanilla on medium speed until pale, about 1 minute.
6. Once chocolate has cooled, add to mixer bowl and beat on low speed until incorporated.
7. With the mixer on low, gradually add the dry ingredients, mixing until just combined.
8. Remove the bowl from the mixer and using a rubber spatula or wooden spoon, gently fold in chocolate chips.
9. Let batter rest at room temperature for 20. Batter will firm up and will resemble brownie batter, not cookie dough.
10. Using a small cookie scoop, place scoops of dough onto the prepared baking sheets, 6 to a sheet.
11. Bake for 10-12 minutes or until the tops of the cookies appear to crack.
12. Remove the pan from oven and using the back of a spatula, push cookie edges towards center of cookie while hot to created smaller, round cookies.
13. Allow cookies to cool for 10 minutes on cookie sheet before transferring to a wire rack to cool completely before assembling cookie sandwiches.

For Frosting

1. In the bowl of a stand mixer fitted with a paddle attachment, cream together butter, confectioner’s sugar, vanilla and salt on medium speed until sugar in incorporated.
2. Increase to high speed and whip buttercream for 8 minutes until light and fluffy. Stop mixer occasionally to scrap down sides of bowl.
3. Add buttercream to a pastry bag fitted with a large piping tip. Pipe buttercream onto the flat side of one cookie and then gently top with the flat side of another cookie to create a sandwich.