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

In a mixing bowl, cream together softened butter, light brown sugar, and half of the granulated sugar for 2-3 minutes.

Add the egg and vanilla extract, mixing until well integrated.

Gradually add all-purpose flour, hot chocolate mix, cocoa powder, baking soda, and kosher salt, mixing until a dough forms.

Scoop about 1.5 to 2 tablespoons of dough, flatten each scoop, and prepare for filling.

Place 5-6 mini marshmallows in the center of each disc, wrap dough around them, and roll into a ball. Coat with remaining sugar.

Place cookie balls on the baking sheet and bake for 10-12 minutes until tops crack and marshmallows peek through.

Remove from oven and let cool on a wire rack for about 15 minutes.