Melt the chocolate and butter together over the stove or in the microwave. Set in the fridge to cool.
Beat the eggs and sugar together on high speed until pale in color, about three minutes. It will look a bit foamy.
Add the cooled chocolate/butter mixture into the eggs/sugar mixture. Beat on medium-high speed until combined and smooth.
Add the flour, cocoa powder, baking soda and salt and beat together. The dough will be loose. Cover & let chill for 1-2 hours until firm.
Scoop one heaping tablespoon of dough, flatten it into a disc and place it on a parchment paper-lined baking sheet. Repeat this process with all of the dough, ensuring you have an even number of discs.
Take 3-5 mini marshmallows or 1/2 of a large marshmallow and place it into the center of the disc. Take another cookie disc and place it on top of those marshmallows.
Seal the edges of the two discs together so the marshmallows are in the center of the dough. Roll the dough into a ball and put it back on the baking sheet. Repeat this with all the discs.
Bake the cookies for 15-17 minutes at 350 degrees Fahrenheit until the edges are set and the tops of the cookies are crackled. Remove from the oven and let them cool, or enjoy slightly warm!