1. Preheat the oven to 350°F. Place butter in the bowl fitted with the ultrablade knife. Heat at speed 2 at 150°F for 1 minute. Add graham crackers and 1/3 cup sugar. Launch at speed 12 for 30 seconds, scraping down the sides halfway through. Press the mixture evenly into a 9-inch pie plate. Bake for 7-9 minutes or until crust is set. Wash the Prep&Cook bowl.
2. Increase the oven temperature to 400°F. Place the egg yolks and lime zest in the bowl fitted with the whisk. Mix at speed 6 for 4 minutes. Add sweetened condensed milk and launch the dessert program at speed 2 at 185°F for 10 minutes. Add lime juice and mix at speed 2 for 1 minute. Pour filling into the baked crust. Wash the whisk and Prep&Cook bowl.
3. Place egg whites, 1/3 cup sugar and cream of tartar in the bowl fitted with the whisk. Launch at speed 8 at 110°F for 8-10 minutes, without the stopper, or until egg whites are stiff and glossy, but not dry. Spread over the pie filling, sealing edges. Bake 8-10 minutes or until meringue is golden brown. Cool for 30 minutes at room temperature, then refrigerate at least 2 hours before serving.