Drizzle the cold water in little by little and mix with a fork. Stop adding water when the dough begins to form large clumps. You may need less or more ice water depending on your environment.

Form the dough into a ball and put it in a plastic ziplock or plastic wrap. Refrigerate for at least 2 hours or overnight.

In a medium bowl. stir together the cherries, sugar, cornstarch, lemon juice, and vanilla until well incorporated.

Preheat oven to 375F/190°C. Line 2 baking sheets with parchment paper.

Remove the crust dough from the fridge. Unwrap from the plastic and cut the dough into four even segments. Roll segments of dough into balls or tubes shape. Return the 3 segments of dough you are not working with to the fridge so that they do not warm up.

Cut 3 sides of the plastic ziplock as the working space for rolling the dough or you can use lightly floured parchment paper instead. Working one at a time, flatten each segment into a rough circle for about 8-inch/20cm in diameter with a rolling pin.

Add a quarter of chopped chocolate and cherry filling (remove the excess liquid) on the crust, leaving an inch/2.5cm border clear around the edges.

Brush beaten egg around the border. Carefully fold the crust edges up, overlapping them as you go. Try to ensure no cracks remain or the fruit will seep out during baking. Carefully move the galette to the prepared baking pan. Repeat with the remaining 3 segments of dough.

Egg wash the top of the crust with the remaining beaten egg. Sprinkle with coarse sugar (optional).

Bake in the preheated oven for 25-30 minutes until the crust is golden brown.

Remove galettes to a cooling rack for a few minutes to allow the juices to settle before serving.