Step 1

Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper and set aside.

Step 2

Make the cookies: Microwave the chocolate chips in 30-second intervals, stirring well between each spin, until smooth. Set aside to cool.

Step 3

In a medium bowl, whisk the flour, cocoa powder, baking powder, baking soda, and salt until well blended. Set aside.

Step 4

In a large bowl, beat the butter and sugars with an electric mixer on medium-high speed until light and fluffy, 2-3 minutes. Reduce the speed to low and blend in the egg, yolk, vanilla, and melted chocolate.

Step 5

Add the dry ingredients and mix by hand with a spatula until just combined. Do not overmix. If the dough seems very wet/soft, cover and chill for 30-60 minutes. It should be scoopable but soft.

Step 6

Scoop rounded tablespoons of dough onto the prepared baking sheets, spacing them 2 inches apart. Bake for 8-10 minutes until the edges are set but the centers are still fudgy. Let cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.

Step 7

Make the frosting: Melt the butter in a saucepan over medium heat. Whisk in the cocoa powder and buttermilk until smooth. Remove from heat and slowly whisk in the powdered sugar and vanilla until smooth and glossy.

Step 8

Spoon the warm frosting over the cooled cookies, using the back of the spoon to spread it to the edges. Let the frosting set before serving. Enjoy!