Line 9x9-inch pan with parchment/foil, leaving an overhang for easy removal. (see note 3.) Cut butter into tablespoons. Coarsely chop the Oreos.
Melt butter, white chocolate, salt, and sweetened condensed milk together in a thick-bottomed, nonstick pan on the lowest heat setting. Constantly stir with a heat-resistant spatula, scraping the sides and bottom. Do not raise the heat—patience ensures a smooth mixture.
Once ingredients are melted, take the pan off the heat. Mix in the vanilla. Gently fold Oreos into the mixture.
Pour mixture into prepared pan. Using a spatula sprayed with cooking spray, smooth fudge into an even layer. Crush remaining 2 Oreos and sprinkle over top, pressing them gently into the surface. Cover and refrigerate for 3–5 hours, or until the fudge is set and firm.
Lift fudge out of the pan using the parchment-paper overhang. Cut into small pieces using a hot, sharp knife (run knife under hot water and dry it).
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Notes
Note 1: Use high-quality chocolate for better Oreo Fudge taste; recommended brands: Ghirardelli® and Guittard® (not sponsored).Note 2: Use full-fat sweetened condensed milk, not evaporated milk.Note 3: For thicker fudge, use an 8x8-inch pan; photos in the post show a 9x9-inch pan.Storage: Store Oreo Fudge in the fridge in an airtight container; best enjoyed cold within 2–3 days, remains fresh up to 2 weeks. Avoid leaving out to prevent drying.