Line a 9x9" pan with parchment paper.
Blitz Oreos into fine crumbs (or crush in a Ziploc with a rolling pin).
Set aside 100g of crumbs.
Mix the remaining crumbs with melted butter.
Press half the crumb mixture into the pan to form a crust. Freeze.
Beat heavy cream and vanilla to stiff peaks. Fold in condensed milk, then the reserved Oreo crumbs.
Pour filling over the crust and smooth. Freeze 1–2 hours until firm.
Top with remaining crumbs, gently pressing down. Freeze 6+ hours or overnight.
Lift out, slice into 8 sandwiches with a hot knife.
Serve immediately or store in the freezer.
