Make the shortbread: Preheat the oven to 350 F. Line a square 8×8” pan with parchment paper. Using a hand mixer, beat together the butter, zest and salt. Beat in the powdered sugar. Fold in the flour. Press the cookie mixture into the bottom of the pan. Bake for 20 minutes, until golden on the edges.
While the crust bakes, make the curd: add ¾ cup pomegranate juice and all the ingredients for the curd , except the tapioca starch, to a pot and cook on medium. Once the butter and sugar have melted, mix the tapioca starch and remaining ¼ cup pomegranate juice and add it to the pot. Continue cooking until the curd becomes thick and registers 170 F degrees. If the shortbread isn’t done yet, leave the curd on very low heat. As soon as the shortbread is done, pour the curd over it through a fine mesh sieve. Return to the oven for 10 minutes, until the curd is just set.
Let the pie cool at room temperature and then set in the fridge. It needs a few hours to be completely cool and set.
The day you plan to serve the pie, make the meringue: set the egg whites in the bowl of a stand mixer fitted with a whisk attachment. Attach a candy thermometer to a pot and boil the sugar and pomegranate juice until the candy stage (250 F). When the sugar is close, begin whipping the egg whites on low until frothy. With the mixture on pour the hot sugar syrup into the egg whites slowly. Let the machine continue whipping until you have a fluffy, white meringue that holds peaks.
Spoon the meringue over the curd and let it set in the fridge for an hour (or more) until it’s time to serve. Slice with a sharp knife (run the knife under hot water and dry it before slicing for cleaner cuts).