Preheat oven to 350 degrees.
Roughly crumble crackers into bowl. Knead in butter and sugar until crumbs stick together, breaking up any large pieces of cracker (but not into dust). Press into 8-inch pie dish and chill for 15 minutes. Bake about 16 minutes until the crust starts browning.
Beat yolks, juice and zest into condensed milk.
Scatter peaches over crust; cover with the filling.
Whip egg whites and tartar until soft peaks form. Add vanilla, salt and sugar, one tablespoon at a time until stiff peaks form. Spread over filling and bake about 18 minutes.
Chill at least 6 hours before serving.