Preheat the oven to 350°F. Line an 8-inch square pan with parchment paper.
In a medium saucepan, melt the butter over medium-low heat. Whisk in the brown sugar, milk and vanilla and heat for about one minute. Remove the pan from the heat and stir in the graham cracker crumbs. It will be a thick liquid substance.
Lay a single layer of graham crackers to cover the bottom of the prepared pan.
Spoon a third of the graham cracker paste over the graham cracker layer. Carefully spread around.
Followed by a third of the chocolate chips.
Repeat this process three times so that you have three layers of each "ingredient".
Bake at 350 degrees for 14-16 minutes and marshmallows are browned on top. Let S'mores cool in pan. Serve and enjoy.
A good variation is adding 1/4 cup melted peanut butter on top of each brown sugar/butter level to create a peanut butter s'mores.These are best enjoyed after they have been out of the oven for at least an hour so that everything can firm up a bit. If I'm in a hurry, I'll throw the pan in the freezer (on a hot pad) for about 20 minutes before serving if it's still too gooey.