Preheat oven to 300°F (150°C).
In a small bowl, beat egg whites until stiff. Electric beaters make this job easy.
In a separate bowl, beat egg yolks. Then add in condensed milk, lime zest, lime juice and salt and mix until combined well. Fold in beaten egg whites. Don’t overmix.
Pour mixture into the crust. Bake for 15 minutes. Cool to room temperature. Refrigerate for at least 2 hours before serving. Or make it the day before and leave it overnight in the refrigerator.
When ready to serve top with fresh whipped cream. Sprinkle extra lime zest if desired.