Heat oven to 400ºF.
Trim a 1-inch border around 1 piece of puff pastry, reserving the strips. Poke the trimmed piece of puff pastry with a fork to provide an escape for steam, then lightly brush with egg wash.
Using the reserved strips of puff pastry, build a border by lining the strips up with the outside edge of the the trimmed piece of pastry. Dab the strips with egg wash and fold over to form a square.
Cut a 7-by-7-inch square out of the second sheet of puff pastry. Fold it in half and cut vents for steam along the fold.
Shake bread or cake crumbs on drained cherries and let sit for 10 minutes. Spoon cherry mixture onto bottom piece of pastry, using more than you may think necessary to compensate for the pastry puffing. Apply egg wash to the border, avoiding the very edge.
Lay vented piece of pastry on top. Brush with egg wash.
Bake for 30 minutes. Reduce temperature to 350ºF and bake for another 30 minutes. Cool slightly before serving.