First, make a chocolate ganache, which will be the "fudge" in this fudge ripple ice cream.Pour 3 ounces (about 1/3 cup) of the heavy whipping cream into a small saucepan, and refrigerate the rest of the cream until needed.Heat the 3 ounces of cream over medium heat until hot, and just beginning to simmer around the edges. Remove from the heat, and stir the chopped chocolate into the hot cream until the chocolate is melted and the mixture smooths out into a ganache. Set aside to cool at room temperature for 15 minutes.
While the ganache is cooling, get the rest of the ingredients ready and make the ice cream base. In a bowl, use an electric mixer to whip the rest of the cold heavy whipping cream until soft fluffy peaks form that hold their shape.
Add the sweetened condensed milk, sour cream, vanilla and salt, and whip until smooth.
Spread half the ice cream base into a pan (a standard sized loaf pan works well). Drizzle with half the peanut butter and half the cooled ganache.Repeat with the rest of the ice cream, peanut butter and ganache.
Take a knife and gently swirl everything together, taking care not to mix it too much, but to leave visible swirls throughout.
Cover the pan with two layers of plastic wrap (or a lid if the pan has one), and freeze for at least 8-10 hours, or overnight, until firm enough to scoop.