Instructions

Making the Cookies:
Preheat your oven to 350°F (175°C).
Cream together the softened butter and brown sugar until light and fluffy in a mixing bowl.
Beat in the eggs, one at a time, followed by the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, baking soda, salt, and cornstarch.
Gradually add the dry ingredients to the wet mixture, stirring until well combined.
Roll the dough into 1-inch balls and place them on a baking sheet lined with parchment paper.
Bake for 9-11 minutes, or until the cookies are set but still slightly doughy in the center.
Remove from the oven and immediately press half a marshmallow onto the top of each cookie while they are still warm.
Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
Making the Frosting: