1) Juice enough fresh limes so you get 1 cup of freshly squeezed juice and pulp;
2) Open can of sweetened condensed milk (regular or fat free) and pour into bowl;
3) Refrigerate both items in separate bowls until really cold;
4) Stir juice into sweetened condensed milk until thoroughly blended;
5) Pour mixture into ice cream machine and process according to your machine's directions.
I wanted key lime pie yesterday but, as I am the only one in the house who finds it worth living for, I didn't feel like making a whole one that I knew I would eat in one sitting. Plus, I really didn't have the time to make a proper crust (I make a pie crust as I am not a fan of graham cracker crust). So I dug out the can of s/c milk and got to it. I had only the fat-free but this is one of those pantry items I can't really tell apart from full-fat so I keep it in stock because, even though it's loaded with sugar, at least the fat grams are nil. I chilled the juice and milk overnight and made it this morning and I must say that I damn happy with the results. And yes, I licked the bowl, the beater, and the spoon clean, even before breakfast. :-)
It's a very tart mixture, with only the s/c milk for sweetening; I like it that way so I can't really comment on whether--or even how--to add additional sugar. It came out of the machine at a soft-serve texture and I threw it into a plastic container and will see later how--or if--it firmed up. What I also like is that I won't need a honking big portion of this so the sugar overload will be minimal.
I think I might make some lemon melting moments to go with. It's citrus heaven around here today.