Preheat oven to 425°F.
Prepare you pie crust and roll out the bottom crust on a lightly floured surface until it is slightly larger than a 9-inch pie plate. Transfer the pie crust to your pie plate and keep in the fridge until ready to fill.
1 [double pie crust]
Combine huckleberries, sugar, tapioca, lemon juice, lemon zest, and cinnamon, if using, in a large bowl. Toss to evenly distribute the sugar, then let the mixture sit for 20-30 minutes so the tapioca can soften slightly.
5 to 6 cups huckleberries, 1 cup granulated sugar, 4 Tablespoons quick-cooking tapioca, 2 Tablespoons freshly squeezed lemon juice, 1 teaspoon lemon zest, 1/2 teaspoon ground cinnamon
Add the filling to the pie crust, then dot with butter. Roll out the top pie crust and set it over the huckleberry filling. Fold the edges under and crimp in a decorate manner. Brush the top of the crust with the beaten egg and sprinkle with a little sugar.
2 Tablespoons cold salted butter, 1 large egg, Sugar
Bake at 425°F for 20 minutes. Decrease the oven temperature to 375°F and bake for another 30-35 minutes until golden brown on top and the filling is bubbly. You may need to cover the edges of the pie with an aluminum foil shield to protect it from getting too dark.
Cool for 3-4 hours to set up before slicing and serving.