In a medium-sized pot, melt butter over medium heat. Add 4.5 cups of your mini marshmallows and stir with a wooden spoon until they have completely melted. Remove from heat. (You can also use a double boiler if you prefer.)
Add the rice cereal to the butter and melted marshmallows. Fold in until all ingredients are completely combined.
Shape the cereal treats into flat circles. They should be approximately ½" thick and 3" diameter.
Curl each one around a wooden spoon to form the taco shape. Place on lined baking sheet and allow to set.
Once set, add a layer of chocolate buttercream or chocolate frosting in it. Next add a layer of graham cracker crumbs and mini marshmallows. Top with the chocolate syrup (if using) and serve.