Heat oven to 350°FGrease and line 8x8 baking dish with parchment paperWith paddle attachment, beat softened butter in electric mixer until light and fluffy. Add brown sugar, scraping down sides and bottom of bowl to incorporate. Add Egg and Vanilla. Beat again to combine. In separate mixing bowl, combine the dry ingredients: flour, graham cracker, salt, baking powder and ½ cup chocolate chips. With mixer on lowest speed, gradually combine dry into wet ingredients. Stir till just combined and crumbly wet dough is formed. Add ½ cup nutella. Using a rubber spatula stir once or twice, try not to fully incorporate the nutella to the cookie dough. Think nutella ribbons within a chocolate chip cookie. Spoon ½ cookie dough onto prepared baking dish. Press with fingers to form even layer that reaches the sides of panUsing the back of a wet spoon, dollop and spread (doesn’t have to be perfect layer) marshmallow spread. Sprinkle with about ¼ cup of chocolate chips.Spoon, spread and press the other half of cookie dough on top of that. Fluff may peak through top layer, totally fine. Heat ¼ cup Nutella in microwave safe dish, using 15 sec intervals pausing to stir until a loose drizzly consistency. Dollop another 1/4 cup of Nutella over the top of the cookie dough. Use a knife to swirl the dough and Nutella together.Bake for 35 min. Remove from oven and add mini marshmallows. Turn oven to broil and toast the mini marshmallow till golden brown. Should take about 2 min, stay close by and WATCH to prevent burning! (it CAN happen to the best of us!)Remove from oven and let cool. These bars really need to be cool before cutting; otherwise they will be too oozy and melty. Once room temp, slice, dig in and enjoy!