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.