1. In a food processor, combine flour, lemon zest, 2 T sugar, 1/4 t salt and 1 T water and pulse to incorporate the ingredients. Add the egg yolks and butter and process until well mixed and a clump of dough holds together when squeezed.
2. Pat the dough into the bottom and 2 inches up the sides of an 8-inch springform pan. Refrigerate until ready to fill.
3. Preheat oven to 375.
4. Heat the currants and rum in a small pan over medium heat and let the currants sit until they have absorbed most of the rum.
5. Spread the apples over the bottom of the springform pan, overlapping them. Strain the currants, reserving the liquid, and scatter them over the top of the apples. Sprinkle with 1 T of sugar. Bake for 35 mins, or until the apples are tender.
6. Beat the eggs and 1/3 cup of sugar until lemon-colored and thick. Whisk in the sour cream, reserved rum, and a pinch of salt. Pour half the mixture over the apples and bake for 20 mins, or until custard is set. Pour the remaining custard mixture over the custard and bake for 15 mins longer, until the custard is set.
7. Combine the remaining 1 T of sugar with the nutmeg and cinnamon and sprinkle over the top of the cake. Bake again for 10 mins or until the sugar has melted.
8. Remove the cake from the oven and cool on a wire rack before removing the springform sides of the pan. Slide the cake to a serving plate and serve slightly warm or at room temperature.