Place bottom crust in a 9-inch pie plate. Roll out top crust. Refrigerate both while preparing filling.
Place cherries in a large bowl. Toss with sugar and cornstarch and lemon, if using. Immediately transfer to the crust.
Place top crust over the top, cut off the excess and crimp the edges. Cut a small hole in the center of the pie and a few slits around the top crust to allow for steam to release.
Place pie on a cookie sheet for baking to catch any liquid that bubbles over.
Place egg in a small bowl with a bit of water and whisk. Brush over the top of the pie. Sprinkle with extra sugar, if desired.
Bake for 15 minutes at 425°F then lower the oven temperature to 350°F and bake for about 40-55 minutes (see note). I recommend using a pie crust shield during baking to protect the edges of the pie. You may notice some liquid spilling out of the pie, and when it’s done the crust will be lightly golden. The center may still be liquidy, but will firm up as it cools.
Cool COMPLETELY before slicing. It’s even better to chill the pie before slicing.
You can use a store bought pie crust (refrigerated) but the pie will cook closer to 40 minutes. My all butter pie crust takes longer to cook.