In a large bowl, add heavy cream. Using a hand mixer or stand mixer, whip until stiff peaks are achieved, about 3 minutes.
In a separate bowl, add sweetened condensed milk and ½ cup of peanut butter. Stir until combined. Gently fold whipped cream into peanut butter mixture until just combined.
In a small, microwaveable safe bowl, warm remaining ¼ cup of peanut butter for 30-45 seconds, or until melted and thin.
In a 9x5 loaf pan (or other 6 cup container), add ⅓ of ice cream mixture and spread into an even layer. Drizzle with ⅓ of thinned peanut butter. Repeat twice more ending with a drizzle of peanut butter. Cover and freeze immediately for about 4-5 hours, or until firm.
Notes
Depending on the temperature of your freezer, ice cream may need to be frozen overnight to freeze solid.
Peanut butter can be substituted with any type of nut or seed butter for a different flavor.
Ice cream will keep in the freezer for up to three months in a tightly sealed container.