Whisk together the sweetened condensed milk, heavy cream, and vanilla.
Add the lime juice and most of the lime zest. Whisk for about 1 minute until thickened.
Layer the filling and Ritz crackers in two large 9×13-inch dishes (or several smaller dishes), beginning and ending with the filling.
Sprinkle the remaining lime zest over the top.
Refrigerate for at least 2 hours, preferably overnight.
Cut into 40 portions and serve.
