Prepare your pan with non-stick spray. I use a 9x5 pan because I like nice and thick treats but you can use a 13x9 also or whatever you have. Glass is best because they stick less and it's easier to clean.
In a large saucepot on medium-high heat, add the butter and melt completely. I always use a wooden spoon when making rice krispie treats, they are nice and stiff and clean pretty easily.
Once the butter is melted, add the marshmallows and stir constantly until they are fully melted and nice and creamy. Remove from heat immediatly.
Add the cereal and some sprinkles (unless you are suing funfetti mix) and stir quickly to fully mix in. Dump the mixture into your prepared pan and push down with your spoon to spread it all out. At this point, I spray my hands with non-stick spray and push everything down with my hands to get it nice and compact (be careful because the mixture may still be hot!). Add more sprinkles right away to the top and lightly press in with your hands as well.
Allow the treats to cool for at least 20 minutes before serving, longer if you can resist. Enjoy!