- Preheat the oven to 375°F (190°C). 
- Add both types of sugar and room temperature butter into a mixing bowl. Beat for about 1-2 minutes until well-combined. You can use a hand mixer or a stand mixer fitted with a paddle-shaped attachment. 
- Add the egg and vanilla extract. Beat for 1-2 minutes or until well-combined. 
- Stir the flour with baking soda, graham cracker crumbs, and salt in a small bowl. Add the flour mixture to the mixing bowl. Mix over low speed until half-combined (the flour shouldn’t be fully incorporated at this point). 
- Add the chocolate chips (or roughly chopped chocolate) and 2 whole graham crackers crumbled into smaller pieces to the mixing bowl (set the third graham cracker aside). 
- Mix until the chocolate and cookie pieces are evenly distributed and there are no streaks of flour visible. 
- Scoop the dough with a 3 Tbsp scoop (generously), flatten it out in your hand, put 5-6 mini marshmallows in the middle (or 1/2 of a large marshmallow). Wrap the cookie dough around marshmallows forming a ball of dough. The marshmallows should not be visible. Repeat with the remaining dough and marshmallows. 
- Place the cookies at least 2 inches (5 cm) apart on a baking sheet lined with parchment paper. Top the cookies with 3 small pieces of the remaining graham cracker. 
- Bake for 11-12 minutes. The cookies will be still soft (they will finish baking on the sheet pan) and should be golden at the edges. Leave them on the baking sheet to cool. 
- Enjoy!