In a medium-sized bowl, whisk together the sugar, cocoa powder, and salt. Add the evaporated milk, butter, eggs, and vanilla extract, whisking well to combine.
Pour the filling into the unbaked pie shell. Bake for about 45 minutes, or until the filling is set around the edges but slightly jiggly in the center.
Cool the pie on a wire rack. Serve warm, at room temperature, or chilled.