Cut the butter into chunks, place the marshmallows and butter into a microwave safe bowl. Heat for 1 minute to 1 minute 30 seconds.
Remove the bowl from the microwave, stir the marshmallows and butter together until they melted, blended and smooth.
Add the vanilla extract. Stir well.
Pour in the crisp rice cereal, stirring until all the cereal is coated in the melted marshmallows.
Scrape the marshmallow and cereal mixture into the greased 13 x 9 inch pan.
You can spread the cereal around as much as you can, by this time the spoon is probably a sticky mess.
Using wax paper, press the cereal & marshmallow mixture down into the pan, spreading and pressing evenly.
Remove the wax paper. Sprinkle the top with your toppings of choice (unless you are using melted chocolate to drizzle). Gently press the toppings into the treats. Set aside to let set.
If you are melting chocolate chips to drizzle over the top do so in 30 second intervals in the microwave, stirring between each until smooth and melted. Drizzle the melted chocolate over the treats using a spoon.
Once the treats have set up (about 10 minutes tops) cut into squares, serve, & enjoy!