In a small saucepan over medium-low heat, melt together the chocolate chips and butter until smooth. Let cool completely before starting the cookie dough.
In a mixer, combined the eggs, brown sugar, and vanilla until well combined. Mix in the cooled chocolate mixture.
Add in the dry ingredients (not the marshmallows!), until everything is well combined. Place the dough in the fridge for about an hour and a half minimum.
Preheat oven to 325℉ and line 3 baking trays with parchment paper. Scoop the cookie dough into balls about 1 ½ tablespoon in size (you can make these bigger or smaller depending on your preference and how many you want to make!).
Lightly flatten the cookie dough balls, but not too much. Bake for 9 minutes. Remove from oven and add 3-5 marshmallows to the top of each cookie. Gently press the marshmallows into the cookies and return to the oven for another 2 minutes.
Let the cookies cool completely while you make the fudge topping.
Mix together the fudge topping ingredients until smooth. You may need to add more/less powdered sugar-just slowly add it until you have a consistency you like. You want it thin enough to drizzle onto the cookies but thick enough that it doesn't just slide off.
Drizzle the cookies with the fudge topping and let it harden before serving and enjoying!
