Make the Graham Base:

1. Preheat oven to 350F. You will need 2 large sheets of parchment paper that reach over the long edges of your pan. Butter and parchment-line a 13×9 pan, with one of the sheets.  Butter that sheet. Reserve the second sheet.
2. In a large bowl, whisk together the graham crumbs, flour, soda, and salt.  Set aside. Into the bowl of a stand mixer, or using a hand mixer, cream together the butter and sugars until light and creamy, 2-3 minutes. Mix in the eggs, 1 at a time, then add vanilla. Mix until incorporated.
3. Turn the mixer speed to low and slowly add the dry ingredients until incorporated. Divide the dough into halves.
4. Butter your hands and press the first half into the bottom of the parchment lined and buttered 13×9 pan.  This layer will become your top layer of the bars.  Using the parchment, lift it gently out of the pan and set aside.
5. Now line the pan with the second sheet of parchment, allowing the sides to overhang for easy lifting.  Butter that sheet, and pat in the remaining graham dough, making sure it covers the entire bottom of the pan, into the edges and corners.

Add Fillings:

1. Place the chocolate chips or bars over the graham base, covering the bottom as evenly as possible.
2. Place the marshmallows over the chocolate.  If using Marshmallow Fluff, spread it over the chocolate, being careful not to intermix the chocolate with the marshmallow.

Top the Marshmallow:

1. Lift the parchment containing the top crust.  Flip it over the marshmallow and gently spread it to the edges of the pan. If you are using marshmallows instead of fluff (as I did), it might break up a bit.  This is fine!   It will allow some of the marshmallow edges to toast – nothing wrong with that!
2. Put pan into the oven and bake 27-32 minutes, until top is deep golden brown.  The top should be crispy.
3. You can serve these warm or cooled, just realize that when warm, they may be a bit more gooey.