First prepare and bake your the tart crust. Sift flour into a bowl. Add the butter and lightly rub into the flour using your fingertips until there are no more lumps of butter. Add sugar and vanilla seeds. Add an egg yolk, vodka (or milk) and a pinch of salt. Stir to combine, then use your hands and knead until the dough starts to come just together ( it must remain crumbly, do not overwork.) Wrap the dough in a plastic wrap and place in a fridge for about 1 hour.TipWe recommend using vodka instead of milk in this recipe. It evaporates quicker while baking which means the tart crust will be flakier.
Bake the tart crust
Preheat your oven to 175 °C / 350 °F. Lightly dust a clean work surface with flour, flatten the dough into a disk and roll out the tart dough to 0.5 cm / 0.2 inch thickness. Wrap the dough around rolling pin and carefully unroll over a 20 cm / 8-inch tart mold. Prick the dough all over with the tines of a fork, and press the tines up against the edges of the tart plate. Place in the freezer for about 20 minutes. Line the dough with a large piece of parchment paper. Press the paper into the edges of the dough. Fill the parchment paper lined tart dough with pie weights or dried beans. Make sure they cover the entire space. Place in the oven and bake for 15 - 20 minutes, then check if the baking paper sticks. If not, remove the paper with the beans or pie weight and bake for another 10 minutes. Let the tart crust cool on a wire rack.
Add pitted cherriess, sugar and Kirch (optional) to a saucepan. Place over high heat. Cook for about 3 minutes, stirring occasionally then remove from the hear, add corn starch and stir to combine. Strain the cherries and save the juices. Place cherries into a bowl, add another tablespoon of starch and leave them to cool completely.
Using an immersion blender combine all the ingredients for the custard in a bowl. Mix together eggs, sugar, all-purpose flour, starch, whipping cream, buttermilk, vanilla seeds, lemon zest, salt until you get a delicious, silky, runny mixture.
Arrange cherries over the baked tart crust. Pour the custard over the cherries. Drizzle the remaining cherry juice over custard in decorative pattern. Place in the oven and bake for 35 minutes at 160°C / 320 °F, then raise the temperature to 190 °C / 375 °F and bake for another 10 minutes. Remove from the heat and serve the tart at room temperature or cold.