Heat a small one litre saucepan over medium heat and melt butter.
In a medium bowl whisk the sugar and egg yolks together, stir the mixture into the butter. Cook while stirring constantly until slightly thickened for about five to six minutes.
Stir in mamey, lemon juice, rind and refrigerate in a glass bowl for one hour.
Spread half of the ice cream over the bottom of the baked pie shell and transfer to freezer for one hour.
Assemble the pie by spreading half of the lemon mixture over the ice cream, spread remaining ice cream on top of lemon mixture, top with remaining lemon mixture. Transfer to the freezer again for one hour.
In the bowl of a stand mixer attached with a whisk, whip the egg whites with the cream of tartar on medium speed until foamy. Increase the speed to high and gradually pour inthe sugar. Continue whipping until stiff peaks form.
Dollop the meringue on top of the frozen pie while sealing edges. Bake the pie at 425˚F for about three to five minutes (you may also use a kitchen torch to brown the meringue.) Freeze until firm, and serve at once.