Line a 9X13 OR 8X8 glass pan with parchment paper. 9X13 will make for more, thin bars, while the 8X8 will make for fewer, thick bars. Set pan aside.
Using an oven AND stove-safe skillet, melt the butter on the stove over medium-high heat (I use my cast iron!).
Once butter has melted, stir in the vanilla extract. Add in the mini marshmallows and lightly stir to coat.
Turn your oven to broil and place the skillet in the oven. Broil for 1-2 minutes, or until the marshmallows are a toasty light brown. WATCH VERY CAREFULLY. Things can burn in a matter of seconds when broiling in the oven!
Carefully remove from the oven and gently stir in the crispy rice cereal.
Now, you have a couple of options here. You could gently mix in ALL of the crushed graham crackers to the marshmallow rice cereal mixture, OR you could mix in half and save the other half for sprinkling on top of the chocolate drizzle!
Pour or scoop the cereal-marshmallow mixture into the prepared pan. Gently smooth down with a spatula or top with a piece of parchment paper and gently press down to make for more even bars.
Melt your chocolate at 50% microwave power for approximately 2 minutes, or until chocolate is melted, stirring every 30 seconds. Drizzle over the top of the bars.
Allow bars to set for at least an hour, or until chocolate has set. Cut into bars and serve!