Flatten the big piece of dough on a surface sprinkled with flour using a rolling pin until it forms a rectangle measuring 18×13 inches. Put the dough in the pan and fold the edges over the sides. Gently press the dough into the inside and corners of the pan. Put the pan in the fridge or freezer while you flatten the second piece of dough into a 16×11-inch rectangle (make sure to keep the dough in the pan as cold as you can).
Take the pan out of the fridge or freezer. Pour the apples and their juices onto the dough in the pan. Even though it might look like a lot of apples, they will shrink as they cook. Put the second piece of dough on top of the apples. Cut the dough so that both the top and bottom edges extend about ¾-inch beyond the pan. Close the edges firmly using your fingers.
Apply heavy cream or egg wash on the top of the dough. With a sharp knife, make many 1-inch cuts on the top of the dough to let the steam out while baking. Put the entire sheet on a bigger baking tray – some things might spill, and it’s better to catch them on the larger tray than on the bottom of your oven.
Bake for 40 to 45 minutes until the top is a nice golden brown and the filling is bubbling through the holes in the crust. Let the pan cool on a metal rack for at least 45 minutes before cutting and serving.
