On a lightly floured work surface, roll 1 disk of dough to 1/8 inch thick. Fit into a 9-inch deep-dish pie plate. Trim edges flush with rim. Refrigerate for 1 hour.
Roll remaining disk of dough to 1/8 inch thick. Using a 1 3/4-inch fluted round cutter, cut out about 70 rounds, rerolling scraps if necessary. Place rounds on a parchment-lined baking sheet, and refrigerate for 30 minutes.
Peel and core apples. Thinly slice half the apples, and cut remaining apples into 1-inch pieces.
Toss together apples, lemon zest and juice, sugars, flour, salt, cinnamon, and nutmeg in a large bowl. Place filling in piecrust, mounding it in the center. Dot with butter. To make egg wash, whisk together egg yolk and cream in a small bowl. Lightly brush edge of piecrust with egg wash.
Arrange dough rounds over filling, working in a spiral from the outside in to the center, overlapping them slightly. Lightly brush top of each round with egg wash as you work to help them adhere to one another.
Once the filling has been covered with rounds, lightly brush entire top of pie with egg wash.
Sprinkle top with sanding sugar. Refrigerate pie for 1 hour.
Preheat oven to 400 degrees, with racks in middle and lower positions. Place a foil-lined baking sheet on lower rack to catch any juices. Place pie on middle rack, and bake until crust begins to turn golden brown, about 25 minutes. Reduce oven temperature to 375 degrees, and bake until crust is golden brown and juices are bubbling, about 1 hour, 10 minutes more. Tent with foil if crust browns too quickly. Let cool completely on a wire rack.
