In a large bowl, gently toss the blackberries with the sugar, flour, lemon juice, lemon zest (if using), cinnamon (if using), and nutmeg (if using). Let the mixture sit for about 15 minutes to allow the flavors to meld.
Assemble the Pie:
Preheat your oven to 375°F (190°C)
On a lightly floured surface, roll out one of the dough disks into a 12-inch circle. Transfer it to a 9-inch pie dish.
Pour the blackberry filling into the crust, spreading it out evenly. Dot the filling with the small pieces of butter (optional).
Roll out the remaining dough and cut into strips to make a lattice topping on the pie.
Bake the Pie:
Place the pie on a baking sheet to catch any drips and bake in the preheated oven for 30 minutes at 375°F (190°C).
Add the Finishing Touches:
In a small bowl, whisk together the egg and water to make the egg wash. Brush it over the top crust. If desired, sprinkle with coarse sugar for a sparkling finish.
Finish Baking the Pie:
Return the pie to the oven and bake for an additional 30 minutes at 350°F (175°C), or until the crust is golden brown and the filling is bubbling.
Serve your wild blackberry pie warm or at room temperature, with a scoop of vanilla ice cream or a dollop of whipped cream for a truly indulgent treat.