Chill the cream, beater and a deep mixing bowl for at least 24 hours.
Add condensed milk, vanilla and cocoa to another mixing bowl. Whisk well and make a smooth lump free chocolate mixture.
Pour the chilled cream to the chilled bowl and begin to whip it - initially on a low speed to avoid splashes. Later, on a medium speed until stiff peaks.
Gently fold in the chocolate condensed milk with the whipped cream until no streaks appear. Transfer the mixture to a freezer safe container (a metal container if possible) and freeze until set.
Scoop chocolate ice cream and serve.