Place sweetened condensed milk in a large bowl, sift in cocoa powder*. Stir to combine.
Fold in whipped cream and chopped chocolate.
Put into a container and freeze until firm.
Notes
*You can use chocolate chips, if you prefer. *I sifted the cocoa powder to ensure the smoothest texture possible, you can skip this step if you'd like.
Recipe by Crumbs and Chaos at http://www.crumbsandchaos.dreamhosters.com/2015/05/double-chocolate-ice-cream/