In a medium sized bowl whisk together two 14oz. cans of condensed milk, 1 cup of key lime juice, and 2 eggs. Pour filling into prepared pie shell (if you made the pie shell, make sure it is COMPLETELY cooled before pouring filling). Bake in the oven for 15 minutes. Cool pie on rack for 15 minutes then cover pie and move it to the refrigerator to chill for at least 2 hours.
Once chilled, it's time to make the topping. Whipped cream? I don't think so. Meringue? How prosaic. No, this is what puts Nellie and Sal's Key Lime Pie over the top! Are you ready for this? Combine 1 cup of low fat sour cream and 2 tablespoons of powdered sugar. Spread over the top of the pie, sprinkle a teaspoon of lime zest as a garnish on top and serve chilled.