For filling: Beat cream cheese and sugar till smooth. Beat in egg and vanilla; then stir in Oreos. Set aside.
For brownies, beat butter, sugars, and cocoa till well combined and smooth. Mix in eggs and vanilla.
Stir in flour, then Oreos.
Spread batter into a well greased 9x13" pan. (I like to line mine with foil.) Pour filling over the top and spread evenly. Swirl with a knife or spoon handle.
Bake at 350° for about 40-45 minutes or till toothpick comes out with moist crumbs. Cool completely before serving.