How to Make It
Combine huckleberries and butter in a large saucepan over medium-high, and bring to a simmer, stirring often. Reduce heat to medium-low to maintain a gentle simmer, and cook, stirring often, until berries have thickened and mixture has reduced to 3 cups, about 25 minutes. Transfer to a large bowl; let cool 30 minutes. Add 11/2 cups sugar, flour, salt, and, if desired, sumac and violet extract; stir to combine. Chill until ready to use.
Preheat oven to 425°F with rack in lower third of oven. Place a rimmed baking sheet in oven (do not remove pan while oven preheats). Line a 91/2-inch deep-dish pie plate with 1 pie crust. Chill 20 minutes.
Spoon huckleberry mixture into chilled crust. Top with remaining pie crust. Trim edges, and crimp to seal. Lightly brush top crust with egg wash, cut vents in crust, and sprinkle with remaining 1 tablespoon sugar.
Place pie plate on preheated baking sheet, and bake at 425°F for 15 minutes. Reduce oven temperature to 350°F, and bake until crust is golden brown and filling is set, about 1 hour and 15 minutes. Loosely cover with foil after 35 to 40 minutes to prevent overbrowning. Place pie on wire rack to cool completely, at least 4 hours.