To make the filling, strain the cherries, reserving their juice, and set aside the cherries in a separate bowl. Pour 1 cup of the cherry juice into a saucepan. Add 4 cups sugar, place over low heat, and stir gently until the sugar is completely dissolved. Raise the heat to medium-low and continue to stir until the mixture comes to a slow simmer. Skim any foam that forms. Simmer the syrup gently for 10 minutes, or until it reaches 220F on a candy or jelly thermometer.
Add the cherries and lemon juice to the syrup and cook gently over low heat for 10 to 15 minutes, allowing the mixture to thicken. You don't want the syrup to caramelize, so keep the temperature just below 223F. The syrup should be bright red, moderately thick, and clinging to the fruit, but take care not to overcook. Remove from the heat and allow the syrup and cherries cool to room temperature. (If you like, to test the thickness of the syrup, pour a tablespoon or two onto a small plate and place in the refrigerator. Chill for 15 minutes. Remove from the refrigerator. The syrup should be thick, not runny, with a deep red color. If the syrup seems thin, return to 220F and cook for another 3 to 5 minutes.) Transfer the cherries and syrup to a covered container and refrigerate for several hours or overnight, allowing the cherries to absorb the syrup and to become plump.
To make the dough, in the bowl of a stand mixer fitted with the paddle attachment, beat the butter at medium-high speed until it is light in color and fluffy, 5 to 7 minutes. Meanwhile, sift together the flour, baking soda, and salt into a separate bowl. Set aside. Add 1/2 cup sugar to the creamed butter and mix thoroughly. One at a time, add the egg, vanilla, and 1 teaspoon of the lemon zest, thoroughly incorporating each addition. Slowly add the sifted dry ingredients, blending them into the butter mixture thoroughly without overworking the dough.
Scoop the soft dough onto a piece of plastic wrap, covering the dough loosely but completely. With a rolling pin, roll the dough into a round disk. (The plastic wrap will be tight around the dough.) Let the dough rest in the refrigerator for one hour or more.
When the dough is firm to the touch, unwrap it and roll it out evenly on a lightly floured surface into a 12-inch round. Drape the round over a 10-inch fluted tart pan with a removable bottom and gently press the dough into the bottom and up the sides of the pan. Trim the top edge of the tart by running a rolling pin over the fluted edge of the pan. (You can fill the tart shell with the cherry mixture and bake it right away, or cover the unfilled, unbaked shell and refrigerate until you're ready to add the cherry mixture and bake your torte.)
Preheat the oven to 350F.
Pour the cherries and syrup into a strainer set over a large bowl, allowing most of the syrup to separate from the fruit. Pour the cherries with the syrup clinging to them into the unbaked tart shell, spreading them evenly over the entire surface. Sprinkle the remaining 1 teaspoon lemon zest evenly over the cherries. Add 3 or 4 tablespoons of the fruit syrup, spreading it evenly over the cherries; the shell should be barely half full. Store the remaining syrup in the refrigerator.
Bake until the torte is light golden brown around the edges, 15 to 20 minutes. Remove from the oven and transfer to a wire rack to cool. Serve at room temperature.
Cat's Note:
This recipe requires a bit more technical proficiency than the other recipes in this section. Sour cherries are notoriously tricky to cook into syrup. In Greece, where home cooks often make their preserves without the help of a thermometer, it's common for the syrup to stubbornly refuse to thicken. In Greek villages, a common way to say "What's the matter?" is '"Den sou edese to vissino?"' Literally translated, this means, "Did your preserves not thicken?"
