Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a medium bowl, sift together flour, cocoa powder, baking soda, baking powder, and salt. Whisk until combined.

In a large bowl, whisk together melted butter, brown sugar, white sugar, vanilla, egg, and egg yolk until smooth.

Slowly add the dry ingredients to the wet mixture. Fold until just combined.

Let the dough rest for 10 minutes.

Use a cookie scoop to portion the dough and roll into balls. Roll each ball in granulated sugar.

Bake for 6 minutes, press a half marshmallow on top, then bake for an additional 2-3 minutes.

Cool on the sheet for 2 minutes, then transfer to a cooling rack and top with a Hershey's Kiss.