Lightly grease or spray your baking dish with nonstick spray and line with parchment paper.
In a large saucepan over medium heat, melt the butter, stirring often, until it starts to caramelize and develops a pleasant nutty aroma (about 4–5 minutes).
Reduce heat and stir in the marshmallows until completely melted and smooth.
Remove pan from heat and stir in the vanilla extract.
Scoop the marshmallow mixture evenly into 3 separate bowls. Add a few drops of food coloring to each bowl (one purple, one orange, one green). Stir well until the colors are vibrant, adding more food coloring as needed.
Divide the crispy rice cereal evenly among the three bowls (2 cups cereal per bowl). Stir until the cereal is fully coated in the colorful marshmallow mixture. Also stir in 1/4 cup crushed Oreo cookie pieces into each bowl.
Press the purple mixture evenly into the bottom of your prepared pan. Gently spread and press the orange cereal mixture on top of the purple layer. Finally, top with the green cereal layer. Use buttered hands or a greased spatula to press each layer down firmly and evenly.
Top with extra oreos and the edible eyes, pressing gently so they stick to the rice krispie treats.
Chill in the fridge for 1 hour until firm.
To serve, lift the parchment paper to pull the rice krispie treat slab from the pan so you can cut into squares.
Video
Notes
Nutrition information is an estimate only.Store rice krispie treats in a single layer an airtight container at room temperature for 3-4 days. If you need to stack them, place a sheet of parchment paper between the treats so they don't stick together.