Preheat the oven to 350ºF.
Using a small, pourable bowl (like a Pyrex one), melt butter and whisk in sugar. Stir until combined. In a chopper, or by hand, add graham cracker crumbs to a bowl and pour butter mixture on top. Stir to combine. (It will look like sand).
Coat a 9x13 pan with cooking spray. Press graham mixture on the bottom, evenly. Bake for 10 minutes.
Meanwhile, pour the brownie mix into bowl (you can use the same one!). Add coconut oil, bacon grease, eggs and water. Mix until combined, about 1 minute. Add peanut butter chips.
Once graham crust is finished, pour brownie mix over. Bake for an additional 25 minutes. Sprinkle with mini marshmallows and bake for a final 5 minutes.
Remove from oven and allow brownies to cool for 20 minutes before cutting. They will be fudgy and gooey.