Line your 9x9-inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a microwave-safe bowl or double boiler, combine the white chocolate chips, semi-sweet chocolate chips, and sliced butter. Heat in 30-second intervals, stirring in between, until everything is melted and smooth.
Once the chocolate mixture is melted, remove it from heat and stir in the sweetened condensed milk until well combined.
Mix in the vanilla extract and red food coloring. Adjust the amount of food coloring based on how vibrant you want the fudge to be.
Gently fold in the mini marshmallows and crushed Oreos, ensuring they are evenly distributed throughout the mixture.
Pour the fudge mixture into the prepared baking pan, spreading it evenly with your spatula. Smooth the top for a polished finish.
Refrigerate the fudge for at least 2-3 hours, or until it is completely set.
Once set, use the parchment overhang to lift the fudge out of the pan. Cut into squares and serve!
