1. Make the chocolate ganache. In a small saucepan on the stove, or in the microwave, warm 1/4 cup of the cream until hot, but not boiling. Place the chocolate chips in a small bowl, then pour the hot cream over top of the chocolate. Allow it to sit for 1 full minute before stirring the mixture until smooth and creamy. Set aside.
2. Pour the can of condensed milk into a large mixing bowl, then use a small whisk to combine the cocoa powder with the condensed milk, whisking until fully incorporated and smooth. Set aside.
3. Crush the cookies. Using a food processor, crush 10 of the cookies into fairly fine crumbs. You can also place the cookies in a resealable bag and crush them using a rolling pin. Chop the other 10 cookies into larger pieces. Set aside.
4. In the bowl of a stand mixer fitted with the paddle attachment, or using a handheld electric mixer, whip the remaining whipped cream on high until stiff peaks begin to form, about 3 minutes. Pour the chocolate condensed milk mixture into the whipped cream, along with the crushed AND chopped cookies. Use a spatula to combine everything, folding it all together until incorporated.
5. Layer the ice cream into a freezer-safe container or loaf pan, alternating the layers with spoonfuls of the chocolate ganache, giving the ganache a bit of a swirl with a knife. Top off the ice cream with the 2 remaining Oreo cookies, either chopping them up or leaving them whole. Place the mixture in the freezer for 5-6 hours, before scooping and serving. 

Leftover ice cream can be stored in the freezer for up to 2 months, covered.