Line a loaf pan with waxed paper, set aside. And if your freezer is anything like mine, go ahead and take a second to clear a flat surface.
In a large mixing bowl, whisk together the sweetened condensed milk, pumpkin, vanilla, cinnamon, and nutmeg until smooth. Set aside.
In the bowl of an electric mixer, beat the whipping cream on high until stiff peaks form, about five minutes.
Spoon about ½ cup of the whipped cream into the pumpkin mixture. Stir gently until mostly mixed (you're just looking to lighten up the mixture so the rest of the whipped cream can go in easily).
Add the remaining whipped cream, and fold in gently. At first, the mixture will appear lumpy, but the more you fold, the smoother it will get. Don't be aggressive with your folding, just keep at it gently until it's smooth.
Pour the mixture into the prepared loaf pan. Press an additional piece of waxed paper into the top of the mixture to prevent ice crystals from forming.
Freeze for 4-6 hours, or until solid and scoopable.
Notes
You'll want to whip the cream until stiff peaks form—that means the whipped cream holds its shape without collapsing. Anything less and your ice cream will be too soft. Anything more and your ice cream will come out grainy.
Either put the wax paper back on top of the ice cream after serving, pressing it gently into the surface, or transfer the ice cream to an airtight freezer container. This will keep ice crystals from forming in your ice cream over time.