Beat the cold cream until stiff peaks form, about 3 to 4 minutes.
Microwave the peanut butter for 15 to 20 seconds, until pourable.
Whisk together the sweetened condensed milk, peanut butter and salt until smooth. The peanut butter will thicken like it is seizing. That is normal, since peanut butter loves and slurps up liquid.
Whisk in 1/3 of the whipped cream until smooth to lighten the base. Whisk in another 1/3 more gently to keep the air. Fold in the final 1/3 very gently. Do not overmix or it will deflate.
Scrape into a freezer-safe container and smooth the top. Press plastic wrap directly onto the surface. Freeze 4 to 6 hours or overnight.
Let it sit 10 minutes before scooping, so it softens just enough to scoop cleanly.
Video
Notes
Peanut butter: Use creamy conventional peanut butter like Jif or Skippy, not natural peanut butter, so the texture stays smooth.A pinch of salt balances the flavors, but it's optional.