Place a rimmed baking sheet in the oven. Preheat the oven to 350°F.
Fit the pie crust into a standard 9-inch pie plate. Trim, fold, and crimp the edge. Refrigerate for at least 20 minutes.
Spread the pecans on another baking sheet and toast for 6 to 8 minutes, stirring once. Let them cool. Roughly chop 1 1/2 cups and reserve the remaining halves.
Place the chopped chocolate and butter in a microwave-safe bowl. Heat in 20-second intervals, stirring each time, until almost melted. Stir until smooth, then cool for 5 minutes.
Whisk the eggs in a large bowl just until combined. Whisk in the corn syrup, brown sugar, vanilla, and salt.
Slowly whisk the warm chocolate mixture into the egg mixture. Fold in the chopped pecans.
Pour the filling into the chilled crust. Arrange the reserved pecan halves on top. Brush the crust edge with egg wash, if using.
Set the pie on the hot baking sheet. Bake for 50 to 60 minutes, covering the rim with foil if it browns too quickly. The edges should be set and the center should wobble gently without appearing liquid.
Transfer the pie to a wire rack. Cool completely for at least 4 hours before slicing. Add a light sprinkle of flaky salt before serving, if desired.