Brown the butter in a skillet until lightly browned and smells nutty.
Transfer to a heat safe bowl and cool a bit.
Cover and chill in the fridge until solid, 2 hours or make a day ahead to save time.
Beat chilled butter in a mixer.
Add sugars and beat
Add egg, yolk and vanilla to combine.
On low, add flour, cornstarch, baking soda and salt.
Add milk.
Add chips and chill dough 2-3 hours.
Preheat oven to 350 and let dough sit on counter a few minutes until easier to scoop.
Scoop 1½ T. of dough for each cookie onto parchment lined cookie sheets.
Bake 9 mins.
Remove and top with 3 mini marshmallows and one piece of chocolate.
Return to the oven for approx 3 mins.
Remove from oven and add a piece of graham cracker.
After 5 minutes, transfer cookies to a cooling rack to cool completely.
