Prepare a 9-inch/23cm tart pan.
Preheat the oven to 190 °C / 375 °F / Gas Mark 5.
Remove the dough from the refrigerator and divide it into 2 parts (one part should be slightly larger than the other).
Place the bigger part of the dough in the tart pan (put the smaller part back in the fridge). Press the dough with your hands into an even layer on the bottom and the sides of the pan (you can use the bottom of a measuring cup to help flatten the dough).
Arrange the cherries on the dough (they should lay tightly next to each other).
Break the chocolate into smaller pieces, stick it between the cherries.
Make a lattice from the other part of the dough. As there are a lot of ground almonds inside the dough, it‘s not as easy to handle and less flexible than an all-flour dough. It‘s important that the dough is very well chilled. Roll it out on a piece of baking paper and sprinkle with a lot of flour. Roll out the dough to a thickness of approx. 1/4-inch (5mm), cut strips of dough and arrange on the filling. Don't worry if the strips are tearing, just transfer them carefully onto the tart and pinch together, the egg wash will 'glue' the torn parts. Alternatively, if you have less time, you can simply divide the dough roughly into pieces, flatten them, and spread on the filling.
Egg wash: beat the egg and with milk, brush the top of the tart.
Bake the tart for 45-50 minutes, until the dough is baked through and browned, and the filling bubbling. After about 30 minutes, check the dough - if it's already nicely golden cover it loosely with a piece of aluminum foil.
Wait about 10-15 minutes before slicing the tart, so that the filling can thicken up a bit.