https://www.youtube.com/watch?v=xfwi2WEbLbs

400g whipping cream
140g condensed milk
60g cocoa powder

Whip/beat cream until soft and... creamy. Don't over-whip.

Add the condensed milk and cocoa powder. Mix together gently until smooth, don't take too long otherwise the cream will un-whip and go back to being runny.

Dump it into any container you like, cover with cling wrap and push out all the air, then freeze for 4-6 hours.