Refrigerate the bowl and beater attachment of mixer. We want everything cold when preparing the ice cream.
Heat Condensed Milk until warm and add the bittersweet chocolate. Mix until the chocolate melts and a smooth mixture is achieved.
Slightly beat the egg yolks in a bowl. Add a third of the chocolate mixture into the egg yolks and mix until incorporated. Add the yolk mixture into the chocolate mixture and continue mixing. Be sure the heat is at medium low. Do not let the mixture boil or you'll end up with scrambled egg ice cream. Mix for 3 minutes.
Switch off heat and mix in the vanilla extract. Transfer in a bowl and cover with a cling wrap. Refrigerate for an hour to an hour and a half.
Beat the chilled heavy cream until soft peak, about 2 to 3 minutes at medium speed. Fold in a third of the whipped cream into the chocolate mixture. Then, gently fold in the whole chocolate mixture into the whipped cream.
Add the cup of chocolate chips into the ice cream and transfer into a suitable container. Alternatively, you can just add the chocolate chips as a topping when serving the ice cream. Chill for at least 6 hours.