Step 1
Place chocolate chips in the top of a double boiler over simmering water. Stir frequently scraping down the sides with a rubber spatula to avoid scorching until chocolate is melted about 5 minutes. Let cool.
Step 2
Preheat the oven to 350 degrees F (175 degrees C).
Step 3
Whisk flour cocoa powder baking powder cinnamon baking soda and salt together in a bowl until thoroughly combined. Set aside.
Step 4
Combine butter and sugar in a bowl and beat using an electric mixer until light and fluffy. Beat in egg and vanilla extract until thoroughly combined. Mix in melted chocolate until thoroughly incorporated. Stir in 1/2 of the dry ingredients mixing until just combined. Mix in buttermilk. Stir in remaining dry ingredients mixing until just combined.
Step 5
Use a medium cookie scoop to drop rounded balls of dough 1 1/2 inches apart on the prepared baking sheets.
Step 6
Bake in the preheated oven until cookies are just set 8 to 10 minutes. Do not overbake. Remove from the oven and allow cookies to cool slightly on the baking sheets. Do not remove cookies from the baking sheets.
Step 7
Combine butter heavy cream cocoa powder vanilla extract and salt in a saucepan set over low heat. Whisk until butter is melted and frosting is smooth and combined. Mix in powdered sugar 1 cup at a time whisking thoroughly after each addition. Keep whisking over low heat until frosting is smooth and shiny 1 to 2 minutes.
Step 8
Remove chocolate frosting from heat and immediately pour approx 1 to 2 tablespoons over each cookie while still warm. Use the back of a spoon to gently smooth out frosting as needed. Allow cookies to cool and frosting to set completely before gently removing from the baking sheets.