Line 8x8 inch square baking pan with foil, lightly butter. Parchment paper will also work.
Using the bowl from your standing mixer, stir together white chocolate pieces and marshmallow creme. Set aside.
In large saucepan combine butter, sugar, heavy cream, salt and vanilla.
Cook over medium heat constantly stirring until mixture begins to boil.
Boil for 4 minutes, stirring continuously. The mixture burns easily, so make sure to keep stirring.
Remove from heat and pour over chocolate marshmallow mixture.
Place bowl on mixer and beat for 1 minute until chocolate has fully melted.
Remove bowl from mixer and stir in the Oreo cookie pieces. I do this by hand and try to avoid stirring in the fine crumbs. I don't add the crumbs to the fudge as I like a nice separation of cookie chunks and white fudge.
Pour into baking pan and chill in the refrigerator until set (at least 4 hours)
Cut into delicious bite sized pieces!