Crush your Oreos however you like. I just put them in a baggy and mash them with a rolling pin, but you can blitz them in a food processor, go to town with a hammer, or anything else you want.
20 Oreo Cookies
In a bowl, mix a handful of the cookies and the heavy cream. Whip this up with a rubber spatula or mixer until soft peaks start to form, almost like whipped cream.
2 Cups Heavy Cream
Add the condensed milk to the mix and fold it together, mixing it but trying not to over-combine it, which knocks air out of it.
14 Oz. Sweetened Condensed Milk
Add most of the rest of your cookies, reserving a few for scattering on the top. Again, mix this carefully without knocking down the cream too much.
Pour the mix into a loaf pan or whatever other container you want, top it with any remaining Oreo bits, and pop it in the freezer. You'll want to let this freeze for at least 6-8 hours, with overnight working the best. When you're ready, just scoop it like any other ice cream and enjoy!