Make the base. Whip the cream to stiff peaks with an electric mixer or by hand with a whisk (this takes longer but it's doable). Fold in the sweetened condensed milk and the sifted cocoa powder.
Mix. Add a third of the ice cream mix to a bread loaf pan. Randomly spoon over a third of the melted peanut butter. Use a skewer or the pointy end of a steak knife to swirl the peanut butter through the chocolate ice cream base. Repeat twice with the ice cream and melted peanut butter until it's all used.
Freeze. Cover the ice cream with plastic wrap, pressing the plastic into the top of the ice cream to minimize ice crystals from forming. (If they do just brush them off of the frozen ice cream). Freeze for 6 hours or overnight. See notes.
Serve. Serve as is or topped with melted peanut butter and chopped peanuts.
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Notes
Substitutions: Try regular cocoa instead of dark cocoa.Soft Ice Cream: Freeze for at least 6 hours.Hard Ice Cream: Freeze the ice cream overnight.To Serve: Let the ice cream sit on the counter for 10 minutes before serving to make it easier to scoop. Top with melted peanut butter and peanuts - optional.