PREP: Line a 9x9-inch pan with parchment paper, leaving an overhang for easy removal (or line with foil). (See Note 2.) Do not skip this step or you probably won't be able to get the fudge out looking very nice. Cut the butter into 1-tablespoon-sized pieces. Coarsely chop the Oreos to get 2 cups. Separately, crush 2 Oreos by adding to a bag and pounding with a rolling pin or meat mallet. Set aside for the topping.
COMBINE: In a thick-bottomed, nonstick pan, heat the butter, white chocolate chips, salt, and sweetened condensed milk on the lowest heat setting. Using a heat-resistant spatula, stir the mixture constantly making sure to scrape the sides and bottom. Resist the urge to increase the heat-- your patience will pay off!
ADD FLAVOR: As soon as the butter, condensed milk, and white chocolate chips are melted, remove the pan from heat. Stir in the vanilla extract; mix well. Add in the 2 cups chopped Oreos and gently mix to combine and incorporate the cookies into the fudge.
CHILL: Transfer the mixture to the prepared pan. Spray a spatula with nonstick cooking spray and smooth the fudge into one even layer with a smooth, even top. Sprinkle the crushed Oreos on top and gently press into the fudge. Cover and refrigerate for 3-5 hours or until fudge is firm.
SERVE: Remove from the pan using the overhang of parchment paper. Cut the fudge with a hot, very sharp knife. (Run it under hot water, dry, and then make quick cuts.) I recommend cutting the fudge into small pieces -- it's rich!
STORAGE: Oreo Fudge is best stored in an airtight container in the fridge and enjoyed cold. If it's left out of the fridge for long, the fudge becomes dry. Leftover fudge will stay good 1-2 weeks in an airtight container in the fridge, but we like it best within 2-3 days.