Preheat the oven to 350°F / 175°C. Line a cookie sheet with parchment paper.
Add the butter to a small saute pan or saucepan. Set the butter over medium heat, stirring occasionally until the butter bubbles up, then turns amber in color (this took me ~2 minutes.)
Pour the brown butter into a small mixing bowl and set it to chill in the freezer for 5 minutes. You should be left with 22g of brown butter.**
If you're using a chocolate baking bar, chop it up into small pieces while the butter is cooling down.
Once the butter has chilled, mix in the light brown sugar, granulated sugar, milk and vanilla.
Add in the flour, baking soda, and salt. Mix together just until a few flour streaks remain, then add in your teddy grahams and ~¾ of your chocolate and mix just until no flour streaks remain. Place little scattered dollops of the marshmallow fluff on top of the cookie dough.
Set the cookie dough in the freezer to chill for 5 minutes.
Scoop out all the cookie dough and roll it into one large ball. Top the cookie with extra marshmallow fluff, your remaining chocolate chips and extra teddy grahams. Bake for 14-16 minutes, until the edges are golden brown and the middle of the cookie no longer looks “wet.”
Once the cookie comes out of the oven, use a large bowl to gently form it back into a perfect circle. Immediately press a large marshmallow into the top of your cookie and use a kitchen torch to torch it (optional.)
Allow the cookie to rest on the hot baking sheet for 5-10 minutes before transferring it to a wire rack to cool (or just before enjoying it warm.) Serve and enjoy!