The preparation for the dough
Dissolve the yeast in the water and whisk in the egg.
Combine with the rest of the ingredients in the food processor and mix very briefly: you should still see the pieces of butter.
Let it rest in the refrigerator for at least an hour, until the butter is hard again.
Meanwhile, prepare the filling.
The preparation for the filling
If you are using fresh cherries from the garden, first pit them and place them just under in a light syrup (ratio 1 l water to 80 g sugar). Let it come to a boil, possibly with a small pinch of cinnamon and a bag of vanilla sugar, to taste. Let cool.
Drain the juice from the cherries (from the jar or stewed) and reserve 200 ml of juice.
Heat 150 ml of that in a saucepan.
Dissolve the cornstarch in the remaining 50 ml and stir it into the warm juice. Let cool.
For the finishing
Roll out the dough on a floured work surface until you have a round sheet that is a few centimeters larger than the pie dish.
Place a piece of baking paper in the dish, drape the dough over it, and press it well against the edge.
Roll off the overhanging edges in one motion with the rolling pin.
Brush the edge with a mixture of egg yolk and milk ('doreren'), which helps the strips of dough that will be used as decoration to stick better.
Gather all the scraps into a ball, roll it out, and cut strips of 1 cm diameter and 6 cm long with a serrated wheel or a pizza cutter.
Press the start of a strip against the top edge of the pie, let it hang down in an arc, and press the other end 4 cm further against the edge. Start a second arc in the middle of the first and continue placing all the strips until the entire edge is covered with overlapping arcs of dough. It should be well covered: a cherry-elderberry pie with so much juice needs a thick, sturdy edge.
Also brush the arc edge with the mixture of egg yolk and milk again for a nice shiny effect.
Put the pie dish with the dough back in the refrigerator until the butter is hard again. If you don't do this, the dough will shrink during baking and the cherry juice will leak out.
Preheat the oven to 170 °C.
Take the pie out of the refrigerator and sprinkle the cherries and the raw elderberries on top. Pour the juice over it.
Bake for 18 minutes and let cool.
