Wash and push the autumn olives through a food mill to remove the seeds. Save the pulp. You can freeze it if you have more than you need for this recipe or use it for jam.
Chill the pie crust in the fridge for two hours before baking.
Preheat oven to 375 degrees Farenheit. Bake your fork-pricked pie crust partially for about 15 minutes with parchment paper and dried beans lining the bottom.
Lower temperature to 350 degrees Farenheit.
Make the filling. First add the egg yolks into a bowl and whisk them. Set aside. Whisk the water, granulated sugar, cornstarch, salt, autumn olive pulp, and lemon zest together in a saucepan over medium heat.
Once it has thickened and bubbled, whisk and reduce temperature to low. Slowly to avoid causing thick egg pieces, add the warm mixture to the egg yolks. Then slowly add the egg yolks to the saucepan. Turn the heat back up to medium. Cook until the sauce is thick and bubbly. Remove from heat and whisk in the butter.
Pour the filling into the partially baked crust. You can set it in a warming drawer or quickly make the meringue. Don't let it cool too much though.
For the meringue, beat the egg whites and cream of tartar for about four minutes until soft peaks form.
Add the sugar, salt, and continue beating until stiff peaks form.
Spread the meringue carefully on top of the autumn olive filling. Spread to the crusts.
Bake for about 25 minutes until the meringue is tinged with light brown. Be careful not to overcook!
Chill at room temperature for one hour then another few hours in the fridge before eating.