Preheat oven to 325F and adjust oven rack to middle position
Make the crust. Process animal crackers, sugar and salt in a food processor or crush by hand with a rolling pin until the crackers are finely ground. Add melted butter and mix until combined. Transfer crumbs to a 9-in regular pie plate.
Using the bottom of a large spoon or measuring cup, smooth the crumbs and firmly press into the bottom and sides of the pie plate. Bake until the crust is fragrant, about 12-14 minutes. Let cool completely, about 30 minutes.
Make the filling. Whisk all the ingredients in a bowl until fully combined and smooth. Leave to rest while the crust is cooling. When crust is cooled, pour the filling into the pie plate.
Bake the pie until most of the custard is set and the center jiggles when lightly shaken, about 15-17 minutes. Remove from oven and let cool completely before chilling. Chill the pie in the refrigerator at least 3 hours. If chilling for longer or overnight use a greased plastic wrap to cover the pie.
When ready to serve, make the whipped cream. Whisk cream, sugar and zest until stiff peaks form.
Serve chilled pie with the whipped cream, a different whipped topping or no topping at all.