Preheat the oven to 350 degrees F. Line 2 large baking sheets with parchment paper.
Place the chocolate chips in a microwave-safe bowl. Microwave in 20-second increments, stirring in between, until melted and smooth. Allow to slightly cool down.
Whisk together the all-purpose flour, cocoa powder, baking powder, baking soda and salt in a medium bowl. Set aside.
Place the salted butter, granulated sugar, and brown sugar in a large bowl. Using an electric mixer, beat on medium-high speed until combined and fluffy. Add the egg, vanilla extract, and melted chocolate. Continue to beat until well combined.
Gradually beat in half of the flour mixture, then the buttermilk, then the remaining flour mixture until smooth.
Drop two rounded tablespoonfuls of dough onto the prepared baking sheets, placing 2 inches apart. Bake cookies for 10 minutes. (Don’t over-bake.) Allow to cool directly on the baking sheets.