Line an 8x8” baking dish with parchment paper, leaving paper hanging over the sides for a sling. Lightly spray the parchment paper with cooking spray.
Chop 20 Oreos into quarters and set aside in a medium sized bowl. Quarter the remaining 10 Oreos, and place those pieces in a separate bowl.
Break the white chocolate into chunks and add it to a saucepan along with the sweetened condensed milk. Cook on low heat, stirring frequently until all of the chocolate is melted.
Once melted and smooth, remove the white chocolate mixture from the heat and pour it over the bowl of 20 Oreos. Stir until the chopped Oreos are coated in fudge.
Pour into the baking dish and use a spatula to make an even layer.
Top the fudge with the remaining 10 chopped Oreos. Gently press the Oreos into the fudge to stick.
Chill the fudge in the fridge for 1 1/2 hours until set. It should be firm and not sticky.
Once the fudge has set, cut it up and enjoy!