How to Make It
Beat butter in a stand mixer fitted with the paddle attachment on high speed until light and fluffy, about 2 minutes. Add sugar, egg yolks, vanilla, and salt. Beat on medium speed until combined, about 1 minute, stopping to scrape down sides as needed. Add flour; stir until dough just comes together.
Coat an 8-inch springform pan with cooking spray. Transfer dough to pan, and pat evenly into bottom and 11/2 inches up sides, flouring hands to prevent sticking if needed. Cover and chill at least 30 minutes or up to overnight.
Preheat oven to 325°F. Stir together cream cheese and 1/2 cup sugar in a bowl until combined. Add egg yolk and potato starch; stir to combine. Set aside.
Place 1/2 cup currants in a small bowl; sprinkle with 1 tablespoon sugar, and set aside. Process remaining 1 1/2 cups currants and remaining 2 tablespoons sugar in a blender until smooth, about 1 minute.
Stir together cream cheese mixture and currant puree in a large bowl until combined. Beat egg whites in a stand mixer fitted with the whisk attachment on medium speed until soft peaks form, about 3 minutes. Fold into cream cheese mixture.
Gently scrape mixture into prepared crust, smoothing top. Bake in preheated oven until filling is puffed, about 1 hour. Let cool completely on a wire rack, about 1 hour and 30 minutes. Remove sides of springform pan, and transfer cake to a platter. Spoon reserved sugared currants over top. Serve at room temperature.