Line an 8x8 inch baking pan with parchment paper. Lightly spray the parchment with cooking spray and set aside.
Melt the butter over medium heat in a large saucepan. Once melted, add the marshmallows. Stir the mixture until the marshmallows are completely melted.
Remove from heat, then immediately stir in the cinnamon, brown sugar, vanilla extract and salt. Finally, fold in the cereal. Make sure all of the cereal gets coated with the marshmallow mixture.
Transfer mixture to prepared pan. Wet your fingers and gently spread mixture to fit the pan. Re-wet fingers as needed to keep the mixture from sticking to hands. Do not pack it down too tightly, just lightly press down so it’s secure in the pan.
Allow treats to set for at least 1 hour at room temperature.
Once completely cooled, lift the rice krispie treats as a whole out of the pan using the parchment paper. Transfer treats to a cutting board or work surface. If you like, you can drizzle a simple powdered sugar or cream cheese glaze over top of the treats but this is totally optional.
Using a teaspoon, sprinkle dots of purple, green and gold sanding sugar over treats, one color at a time, being careful not to mix colors. I like to create small dots of each color all over treats so that you get all of the colors in each treat when cutting.
Cut treats into squares and enjoy!