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

In a large mixing bowl, beat together ½ cup unsalted butter, ½ cup granulated sugar, and ½ cup brown sugar until light and fluffy.

Add 1 egg to the mixture and mix until fully incorporated.

In a separate bowl, whisk together 1 ¾ cups all-purpose flour, ⅔ cup cocoa powder, ½ teaspoon baking soda, and ½ teaspoon salt. Gradually mix this into the wet ingredients.

Fold in 1 cup mini marshmallows.

Scoop spoonfuls of the cookie dough onto the prepared baking sheet, leaving space between each.

Bake for 10 minutes, adding extra marshmallows on top halfway through.

Let the cookies cool on the baking sheet for a few minutes before transferring to a wire rack.

Prepare chocolate ganache and drizzle over cooled cookies.

Enjoy warm or store in an airtight container.