Preheat oven to 300 degrees F (150 degrees C). Butter a 9-inch pie pan.
Beat egg whites in a glass or metal bowl until foamy. Gradually add sugar and vanilla extract, continuing to beat until soft peaks form. Lift your beater or whisk straight up: the egg whites will form soft mounds rather than a sharp peak.
Fold crackers and walnuts into egg mixture; pour mixture into the prepared pie pan.
Bake in the preheated oven until pie is set in the middle, about 30 minutes. Cool pie completely in a wire rack.
Fold coconut into whipped topping in a bowl. Top cooled pie with coconut whipped topping.