Preheat the oven to 300 degrees F (150 degrees C).
In a medium bowl, mix together the ricotta cheese, cream cheese, flour, salt, vanilla, lemon zest and eggs. In a separate bowl, whisk together the egg whites and sugar. Pour into the cheese mixture, and mix until well blended. Roll into balls about the size of a golf ball, and place in a glass baking dish.
Bake for 45 minutes in the preheated oven, or until golden brown on top.
