Spray a 9X13 pan with a non-stick cooking spray and set aside.
Add butter and marshmallows to a large saucepan.
Once the ingredients are melted and combined, remove the saucepan from the heat and gradually stir in Rice Krispie cereal until evenly coated.
Gently fold in red and green M&Ms and Christmas sprinkles, reserving some for topping.
Press the mixture into the 9X13 pan. I spray a piece of parchment paper with non-stick spray and use that parchment paper to press the cereal down into the baking dish.
Then top with the reserved M&Ms and sprinkles. Gently press these down so that they stick into the Rice Krispie treats.
Let the Rice Krispie treats sit at room temperature for 1 hour and then they are ready to slice, serve and enjoy!
Notes
Store any leftover Rice Krispie treats in an airtight container at room temperature for up to 1 week. Do not store these treats in the refrigerator. They are best left to cool at room temperature so that they remain gooey and delicious!