Line a 9”x9” baking pan with foil and lightly spray with non-stick cooking spray. Set aside.
Melt the butter in a large pot over medium heat, until melted.
Stir in marshmallows (reserve 1 cup to stir in at the end) and keep stirring until the marshmallows have melted and are smooth.
Remove from heat and stir in the vanilla extract, puffed rice, cocoa puffs, and golden grahams cereals until the cereal is coated. Stir in 1 cup of reserved marshmallows. Pour mixture into the prepared pan and use a piece of parchment paper to gently press into pan.
Sprinkle the top with extra cereal pieces and let cool. Remove treats from pan and cut into squares. Enjoy!