Start by browning the butter on low heat until it changes color and becomes fragrant. Whisk it with the sugars until they’re well combined (about 3-5 minutes). Add the egg and vanilla, whisking for another 1-2 minutes until a creamy mixture forms.
Use a processor or blender to grind the graham crackers. Add them to the batter and whisk until combined.
Sift in the dry ingredients and gently fold with a spatula until halfway combined.
Add the chopped chocolate and graham crackers, continuing to fold until the dough just comes together. Be careful not to overmix.
Gently scoop the dough into balls using a 2-tablespoon scoop. No need to press too hard. Top with marshmallows if you fancy. Refrigerate for at least 2 hours.
Preheat the oven to 360°F and line 2 baking sheets.
Transfer the cookie dough balls onto the baking sheets and bake for about 12 minutes. The cookies shouldn’t harden all the way; they’ll set more as they cool.
Take them out and give the baking sheets a good smack on the counter to flatten the cookies. Let them rest for 20 minutes, and then it’s time to enjoy your delicious creation!