In the bowl of a stand mixer, cream together the butter, brown sugar, and granulated sugar until light and fluffy, about 3 to 4 minutes.

Add the eggs, egg yolk, and vanilla. Mix until fully combined.

In a separate bowl, whisk together the bread flour, cake flour, cornstarch, baking powder, baking soda, salt, and graham cracker crumbs.

Gradually add the dry ingredients to the wet ingredients and mix just until combined.

Fold in the chocolate chips, chopped Hershey bars, and mini marshmallows.

Using a large cookie scoop, portion the dough into 12 large cookies.

Press half of a large marshmallow into the center of each cookie dough ball and one Hershey's chocolate square onto the top of each.

Place the dough balls on a parchment-lined baking sheet or tray.

Cover and refrigerate overnight.

Preheat oven to 350°F.

Place cookies several inches apart on parchment-lined baking sheets.

Bake for 12 - 14 minutes.

The centers should still look soft when you remove them from the oven.

Allow cookies to cool on the baking sheet for 10 to 15 minutes before serving.

The marshmallow and chocolate will continue to set slightly as they cool.