Preheat the oven to 350°F and prepare a couple of large baking sheets (or several smaller baking sheets) by lining them with parchment paper.
In a large mixing bowl, combine the sugar cookie mix, dark chocolate chips, and cocoa powder.
Using either a hand mixer or a stand mixer, beat in the butter and the large egg until you have a thick dough. This might take about 2-3 minutes. If the dough doesn't come together right away, keep mixing; it will eventually come together.
Please note: this is a super thick dough, that is normal and it may seem crumbly but will come together when you roll them into balls. The heat from your hands will help it come together.
Use a cookie scoop that holds about 1 ½ Tablespoons of dough to portion out balls. Roll each ball in between your hands to about the size of a golf ball.
Place the dough balls on the baking sheets, making sure they are spaced apart at least 2 inches so they have room to spread.
Bake one sheet at a time for 11-14 minutes, or until the cookies start to firm up at the edges.
As soon as you take the cookies out of the oven, press 3 mini marshmallows into the center of each cookie, so they slightly expand.
Put the cookies back in the oven for an additional 2-3 minutes, or until the marshmallows puff up and turn golden around the edges.
Remove the cookies from the oven and let them cool on the baking sheet for at least 5 minutes before transferring them to a cooling rack or a serving plate. Continue with the rest of the cookies and enjoy!
Notes
Please refer to my FAQ’s (Frequently Asked Questions) and ingredient list above for other substitutions or for the answers to the most common questions.
It's normal for this cookie dough to have a very thick consistency.