Here you go, Laura!
To the best that my memory serves me, this is what I did. 🙂
Cream 1 cup butter (room temperature) with 1/2 cup brown sugar and 1 cup sugar. Add 2 eggs and 1-2 tsp vanilla.
Whir (is that a word??) up about a dozen or so full-sized graham crackers in the food processor. Add 2 tsp baking powder, 1/4 tsp salt, and 2 1/2 cups (or so) flour. Basically, it should be cookie dough consistency. 🙂
Press half of the graham cracker cookie dough into the bottom of a 9×13-inch baking dish.
Bake at 350F for about 10 minutes.
Dump a bunch of chocolate chips (maybe 2 1/2 cups?) on top of the dough, so it is pretty much completely covered. Then dump a bunch of mini marshmallows (probably 3 cups) on top of that, until covered.
Take the remaining half of the graham cracker cookie dough and make a sort of “top crust“: I did this by making shingles/puzzle pieces (whatever word works for you!) out of it, pressing small portions between my fingers and laying them on top.
Put it back into the oven for another 10-12 minutes, or until the cookie top is “set” and golden.