In a large saucepan, melt the 1/4 cup butter over medium heat. Keep an eye on it to ensure it doesn’t brown.
Once the butter is melted, add the entire 16oz bag of miniature marshmallows to the pan. Stir continuously until the marshmallows are completely melted and smooth.
Remove the saucepan from heat and gently fold in the 1 box of Hershey's Cookies & Cream Cereal. If you're using them, add in the 1 cup crushed Oreo cookies at this stage as well. Mix until everything is evenly coated with the melted marshmallow mixture.
Line your 9x13 inch baking pan with parchment paper for easy removal (optional). Pour the mixture into the pan and press it down firmly with a spatula or your hands to create an even layer.
Allow the treats to cool at room temperature for about 30 minutes. Once cooled, cut them into squares or rectangles.
Your Cookies And Cream Marshmallow Crispy Treats are now ready to be enjoyed! Serve them at your next gathering or keep them all to yourself for a sweet snack throughout the week.
