In a bowl, combine flour, sugar, and salt. Add cold butter and work it into the flour until the mixture resembles coarse crumbs. Gradually add ice-cold water and mix just until the dough comes together.
Divide the dough into two discs — one slightly larger for the base and one for the lattice top. Wrap and refrigerate for at least 1 hour.
Mix cherries with sugar and cornstarch. Let the mixture sit for about 30 minutes so the cherries release their juices.
Strain off the released juice and simmer it in a saucepan until thickened and glossy. Pour it back over the cherries and mix gently. Let cool slightly.
Roll out the larger dough disc and line a 23 cm deep pie dish (10 cm height). Add the cherry filling.
Roll out the second dough disc and cut into thick strips. Arrange over the filling in a lattice pattern. Trim and crimp the edges.
Brush with egg wash and sprinkle with sugar.
Bake at 200°C for 20 minutes, then reduce temperature to 180°C and bake for 50 minutes, until the crust is golden and filling is bubbling.
Let the pie cool fully before slicing so the filling sets properly.
