In the bowl of a stand mixer with a whisk attachment, beat the whipping cream until the cream forms stiff peaks. Add in 1 can condensed milk, vanilla and peanut butter, and beat until fully combined. Set aside.
In a medium bowl, mix together the butter, cocoa powder, 1 can condensed milk, water, and 1 teaspoon vanilla until fully combined. Pour into a 10 inch springform pan or a 7×11 baking dish. (I have used both, and they are both great. I use the baking dish when there is more people I need to share the cake with.) Sprinkle the crushed oreos on top.
Pour the whipping cream mixture on top, and place in freezer for 4 hours, or until hardened.