Begin by pre-measuring all ingredients and crushing the gluten-free graham crackers, as this recipe will come together quickly. Prepare a 9x9 inch baking dish with parchment paper covering the bottom and sides.
Place 4 cups of mini marshmallows in a large microwave-safe bowl with the butter. Microwave in 30 second intervals until melted, stirring with a coconut oil-greased rubber spatula in between. Will take between 1-2 minutes total time.
Once melted and combined, add in the vanilla extract and mix with the spatula.
Working quickly, add the crispy rice cereal, crushed graham crackers, and additional mini marshmallows to the large bowl with the melted mixture. Fold together with the coconut oil-greased rubber spatula so that everything is evenly coated.
Immediately transfer the mixture to the parchment-lined baking dish. Using the greased rubber spatula, or using your hands covered in coconut oil, firmly press the rice crispy mixture into the pan to form a large square. Allow to sit for 30 minutes to cool.
After 30 minutes, place the chocolate chips or chopped chocolate into a medium-sized microwave-safe bowl. Microwave in 30 second intervals, stirring with a spoon each time, until just fully melted and smooth.
Pour the melted chocolate over the top of the rice crispy block, still in the parchment lined baking pan. Use an offset spatula to smooth the chocolate into an even layer. Allow to rest for another 30 minutes for the chocolate to cool and harden. Place the baking dish in the fridge to speed up this process.
Once the chocolate layer has fulled solidified, remove the parchment paper and rice crispy block from the baking dish. Run a large serrated knife under hot water for 15-20 seconds. This will help to avoid cracking the chocolate. Dry the knife, and carefully slice the block into 16 squares.
Serve and enjoy! S'mores rice crispy treats will keep in an airtight container for up to 3 days.