Position a rack in the center of the oven and preheat to 350 degrees . Generously grease a 9-inch pie pan. In a double boiler, melt the chocolate and butter, stirring until smooth. Let cool.
In a medium bowl, whisk together the flour, cocoa and salt. In a large bowl, whisk the sugar, eggs and vanilla until smooth. Whisk the flour mixture into the egg mixture until just blended. Whisk in the chocolate mixture and 1/2 cup pecans. Transfer to the prepared pie pan and sprinkle with the remaining 1/4 cup pecans.
Bake the pie until a toothpick inserted in the center comes out slightly sticky but not wet, with just a few crumbs clinging to it, about 35 minutes. Let cool completely on a rack.