Preheat the oven to 375° and line a baking sheet with parchment. Then roughly chop graham crackers and chocolate bars. Then tear the mini marshmallows in half and set them aside.

Whisk together flour, baking soda, baking powder, salt, baking powder, baking soda, cornstarch, and salt in a bowl and set aside.

In a separate bowl or the bowl of a stand mixer, beat the butter, granulated sugar, and brown sugar until light and fluffy; 1 to 2 minutes. Then add the eggs and vanilla and continue to mix until combined. Scrape down the bowl before gradually adding the dry ingredients. Mix until just combined.

Set aside a few marshmallows and chopped chocolate bars. Add the remaining marshmallows, chopped chocolate, graham crackers, and chocolate chips to the dough. Mix until just combined.

Scoop dough with cookie scoop or tablespoon (I use a 2-tablespoon cookie scoop) and roll into a ball. Place on the prepared baking sheet spaced 2-inches apart. Add reserved marshmallows and chopped chocolate to the top of the cookie dough.

Bake for 10 to 12 minutes or until the edges of the cookies begin to turn golden brown. Remove from the oven and if necessary. while still warm from the oven, use a round-shaped cookie cutter or glass to bring any wayward marshmallow bits back into the cookie circle shape. Sprinkle a pinch of coarse sea salt if desired. Cool for 5 minutes on the baking sheet before removing to a wire rack to cool.