Break the chocolate bar into chunks and place in a microwave-safe glass bowl. Microwave the chocolate, stopping and stirring every 30 seconds, until melted and smooth. Stir condensed milk into the chocolate. Set aside.
Place the heavy cream in a large bowl and use an electric hand mixer to whip it until stiff peaks form. Fold the whipped cream into the chocolate mixture until completely incorporated. Scrape mixture into an airtight container and cover. Freeze for at least 2 hours before serving.