Preheat oven to 400°F. Prepare a cookie sheet with a nonstick spray.
In a large bowl, using a hand mixer, beat the sugar and butter together until light and fluffy, about 2 minutes.
1 cup granulated sugar, 1 cup unsalted butter
Add the eggs and vanilla; mix until combined.
2 large eggs, 1 teaspoon pure vanilla extract
In another bowl, whisk together the cocoa powder, baking soda, salt, and flour.
⅔ cup unsweetened cocoa powder, 1 teaspoon baking soda, 1 teaspoon kosher salt, 2½ cups all-purpose flour
Add the flour mixture into the wet ingredients and mix until well combined.
Using a medium-sized cookie scoop (about 1½ inches in diameter) or a heaping tablespoon amount, scoop a ball of dough, flatten the dough in your hand to the size of your palm, push the marshmallows into the center, roll up the edges, and form a ball.
180 mini marshmallows
Roll the ball of dough in the ½ cup of granulated sugar and place on a cookie sheet 2 inches apart.
½ cup granulated sugar
Bake for 8-10 minutes, until you start to see the marshmallows poking through the top of the cookie. Allow the cookies to cool for 5 minutes before removing. Cool on a cooling rack or a sheet of parchment paper.