Start by greasing a 9x13-inch baking pan with a little butter or lining it with parchment paper to make removing the treats easier later on.
In a medium saucepan over low heat, melt the 8 tablespoons of unsalted butter. Once melted, add 16 ounces of mini marshmallows (reserve 4 ounces for later) and stir continuously until they are completely melted and smooth. Remove from heat and stir in the 1 teaspoon of vanilla extract.
In a large mixing bowl, pour the melted marshmallow mixture over the 9 cups of Rice Krispies cereal. Gently fold the cereal into the marshmallow mixture until fully coated. Be careful not to crush the cereal too much.
Once the cereal is well coated, fold in the reserved 4 ounces of mini marshmallows and half of the Mini M&Ms. This adds extra texture and makes the treats even more fun!
Pour the mixture into the prepared baking pan. Use a spatula or your hands (but lightly greased!) to press the mixture evenly into the pan. Make sure it’s packed well but not overly compressed.
In a microwave-safe bowl, melt the 8 ounces of chocolate candy melts in 30-second intervals, stirring between each interval until smooth.
Once the Rice Krispie treats have cooled slightly (about 10-15 minutes), drizzle the melted chocolate over the top. Sprinkle the remaining Mini M&Ms on top for a colorful finish.
Allow the treats to cool completely at room temperature before cutting them into squares. This will ensure they hold their shape beautifully.
