Pour the pudding mix into a saucepan. Add the milk slowly and whisk until combined.
Bring to a boil on medium heat, stirring constantly until thickened. Remove from heat and let cool for 15 minutes.
Pour the cooled pudding into the bottom of your 9 x 13 pan making sure it covered completely.
Place a layer of 12 graham crackers, side by side, on top of the pudding.
Add 1 cup of semi sweet chocolate chips on top of the graham crackers.
Sprinkle the dry cake mix on top of the graham crackers and chocolate chips.
Dot with butter slices on top of the cake mix and bake at 350 degrees for 25 minutes.
Remove from oven and stir where there may be dry spots from the cake mix. Place marshmallows on top spreading them out evenly.
Sprinkle the remaining chocolate chips on top of the marshmallows.
Bake for an additional 5-6 minutes or until the marshmallows expand and puff up.
Cool for 15-20 minutes before serving.
Garnish with extra chocolate chips, graham cracker crumbs, whipped cream or ice cream.