Cook purée, eggs, egg yolks, lemon zest, lemon juice, salt, and 1/2 cup sugar in a heat proof bowl set over a saucepan of simmering water (bowl should not touch the water). Stir with a rubber spatula and scrape down sides of the bowl often, until curd thickens and coats spatula, about 8-10 minutes. Let cool until just warm.
Using an electric mixer on medium-high, beat the curd, adding butter a piece at a time and incorporating after each addition, until curd looks lighter in color and texture, about 5 minutes.
Scrape mixture into the crust and chill until firm, about 2-4 hours.
Toss reserved cranberries with sugar. Top pie with sugared cranberries
Garnish servings with whipped cream if desired