1. Preheat the oven to 400°F/204°C.

For the crust

1. Prepare the all-butter crust recipe. Follow the directions to roll out one disc of dough for a 9-inch pie dish. Fit the dough to the bottom and sides of the dish by carefully lowering the dough into the dish and allowing the dough to fall into place.
2. Leave a 1-inch border and trim the rest of the dough using a pair of kitchen shears or a knife.  Crimp the edges and refrigerate.
3. Roll out the top crust to a circle 3 inches larger than your baking dish. Using a pastry cutter wheel (or sharp knife), cut the dough into 1-inch strips. Refrigerate while preparing the filling.

For the filling

1. In a large mixing bowl, combine apple, blueberries, sugar, lemon zest, lemon juice, cornstarch, cinnamon, nutmeg, and salt. Mix well and add to chilled pie crust.
2. Gently lay pie dough strips parallel to each other over the filling allowing for 3/4-inch between each piece.
3. Peel back every other strip halfway and lay a piece of pie dough along the center of the pie perpendicular to the other pieces. Fold the strips back down over the perpendicular strip and fold the other pieces back halfway. Lay another perpendicular strip and repeat the process of threading the strips until the lattice top is complete.
4. Trim away excess dough from the strips to fit snugly with the crimped edge.
5. Brush the lattice top with the egg wash and sprinkle with coarse sugar.
6. Place pie on a baking sheet pan and bake on the bottom third of the oven at 400°F/204°C for 20 min, then reduce oven to 375°F/190°C for an additional 40 min or until pie is browned and bubbly.
7. Allow the pie to cool completely before slicing and serving.