Preheat the oven to 350 degrees.
Cream the butter in a bowl and add both cups of sugar. Mix with a mixer.
Stir in the eggs and vanilla.
Combine the flour, baking soda and salt in a separate bowl and add to the butter mixture; blend well.
Spray a mini-muffin pan with cooking spray.Take this cookie dough, which is really just a chocolate chip cookie recipe without the chocolate chips, and form approximately 1-inch dough balls. Place one dough ball in each mini-muffin cup. Bake for 9 to 11 minutes.
Reduce the oven temperature to 300 degrees.
Let the cookie cups rest for 2 minutes and then use a pestle to indent the cookies. Don't push too far down, as you don't want to use a ton of Nutella to fill the hole. Try to make an indention that one teaspoon of Nutella will fill.
After the cookies are indented, transfer to a cooling rack for approximately 5 minutes. NOTE: you can stop here and save your cookies to fill at another time.
Fill each cookie cup with Nutella and sprinkle crushed graham crackers on top. Place these Nutella-filled cookie cups on a baking sheet that is covered with parchment paper. Then add a marshmallow on top. I use the extra-large marshmallows and cut each into 8 pieces. (I do this to provide more of a sticky surface for the graham cracker to adhere to before I place them back in the oven. It's easier to use a regular-size marshmallow and simply cut it in half, sticky side up.)
Bake the s'more cups for 3 minutes at 300 degrees. After 3 minutes, turn the broiler on high for just 90 seconds (Really, 60 seconds won't brown the marshmallows and 2 minutes is too long; 90 seconds is perfect.).
Remove from the oven and immediately use a metal spoon to press the hot marshmallow down gently.
Serve after 5 minutes.