In a large pot, fill it with a few inches of water. Place it on your stove top and place a tightly fitting glass bowl over top.
Turn stove on to medium-low heat.
Add your butter into the bowl and begin melting it.
When the butter has finished melting, add in your marshmallows and allow them to melt down. Stir often using a rubber spatula to prevent sticking.
Next, add in your peanut butter and vanilla. Fully mix into the marshmallows.
Add your cereal into the sticky peanut butter marshmallow mixture and mix well until everything is fully combined.
Empty your mixture into a well greased 9x12 baking pan, spread it out evenly and set aside.
Place a clean glass bowl on top of your pot of water.
Add your chocolate into the bowl and begin melting it. Stir often using a rubber spatula to avoid burning the chocolate or sticking.
When the chocolate has fully melted, pour it on top of your cereal mixture in the baking tray and spread it evenly across.
Cover your tray and place it into the fridge or freezer for one hour. The bars are ready when the chocolate has completely solidified.
Remove the tray from the fridge and cut the cereal mixture into squares or bars.
Eat!