- In a food processor, combine the flour and salt. Add the butter and pulse a few times, until it forms pea-sized pieces. Add the yogurt and pulse until the dough just begins to hold together. Remove the dough from the food processor and shape by hand into 2 discs. Cover in plastic wrap and refrigerate for 30 minutes.
- On a floured work surface, roll out the dough into two round sheets, 11 inches (28 cm) in diameter each. Line one sheet in a 9-inch (23 cm) pie plate. With your fingers, flute the edges of the pie. Place the other sheet of dough on a baking sheet lined with parchment paper. Refrigerate both sheets of dough.
- In a small bowl, use a fork to lightly beat the egg with the water. Set the egg wash aside.
- With the rack in the lowest position, preheat the oven to 400°F (200°C).
- Using a mortar and pestle or in a coffee grinder, finely crush the tapioca.
- In a bowl, combine the cherries, tapioca, sugar and lemon juice. Spoon into the pie shell.
- Using a flower-shaped cookie cutter, cut flowers from the second sheet of dough and arrange them on top of the cherry filling. Using a pastry brush, brush the dough with egg wash. Place the pie on the baking sheet.
- Bake for 50 minutes or until the crust is golden and the filling is bubbling. Let cool. The pie will keep for 2 days at room temperature.