Preheat the oven to 350 degrees F and line a brownie tray with parchment paper or grease it.
Make the graham cracker crumbs by processing ½ cup of graham crackers in a food processor, or smash them within a bag with a rolling pin. Once done, place to the side.
In a large mixing bowl, beat the softened butter until it is fluffy using an electric mixer. Add in the brown sugar and beat again. It will be gritty.
Add the maple syrup, plant based milk and vanilla extract into the bowl and mix. It will be very wet.
Mix in the graham cracker crumbs (from the food processor), flour, baking soda, baking powder, salt and cinnamon. A soft dough will form.
Gently fold in the chocolate chip then your marshmallows. Mix until all are equally disbursed.
Pour the mixture into baking tray, pressing into the tray and using your hand or a spoon to create an even layer on the top.
Sprinkle the graham cracker crumbs on top and any extra marshmallows and chocolate chips on top.
Bake in the middle rack for 35-40 minutes or until you can insert a toothpick into the center of the cookie bars and it comes out cleanly.
Let cool for 15-20 minutes before cutting into it.