Preheat the oven to 350 degrees F.
Line a baking sheet with parchment paper and scoop eight 1 to 2 teaspoon sized Nutella spoonfuls onto the parchment paper. Place in the freezer while you prepare the dough.
In a standard mixer, combine the butter, brown sugar, hot cocoa powder, egg, vanilla, baking soda, cornstarch and cocoa. Mix together until combined.
Add the all-purpose flour and combine, while also continually scraping down the sides of the bowl.
Once well incorporated, scoop out the cookie dough with a two-inch cookie scoop. Poke a divet in the center of the dough ball and place a frozen glob of Nutella and roll dough around Nutella so no Nutella is showing.
Repeat with all the cookies. Slightly flatten each cookie on the cookie sheet.
Place 3 to 6 mini marshmallows on each individual cookie. I typically start with 3 and then add more if I’m feeling like it!
Bake for 10 to 12 minutes or until the marshmallow is lightly golden. Enjoy with your favorite glass of milk!