Preheat oven to 350 degrees. Line two cookie sheets with parchment paper.

Mix brownie mix, oil, egg, and water in a large bowl with an electric or hand mixer. Beat until it comes together in a thick dough.

Scoop 2 tablespoon scoops of cookie dough onto the cookie sheet. Bake for 8-9 minutes, or until they lose the glossy sheen around the edges but are still a little shiny in the middle. Cool completely before assembling s’mores.

Turn oven to broil. Place graham cracker halves on cookie sheet and top with a large marshmallow. Broil for just a few minutes, until the marshmallow is browned to your liking. Remove from oven and immediately press a brownie cookie on top of each s’more. Cool slightly before eating.