Grease jars with a little butter on the bottom and sides.
Crush graham crackers until fine, I like to use a rolling pin or blender for this, pour graham crackers into the jar until it's about an inch high.
Pour in a layer of prepared brownie mix, about 1 - 1 1/2 inches thick.
Place jars on a cookie sheet or in a bread pan and put in the oven. Make sure you don't preheat!
Set the oven temp according to brownie mix, I set mine at 350 F.
Bake for about 35 - 40 minutes, or until tooth pick comes clean.
Scoop in marshmallow fluff to just below the lip of the jar. Keep jars on baking pan.
Broil on low until fluff starts to brown, about 3 - 5 minutes, keep a close eye on it as fluff will brown and expand in the blink of an eye!
Take out and sprinkle with crushed graham cracker and sprinkles. Let cool for a few minutes and garnish with tags (found here) and string!