Unfold piecrust, and press out fold lines; sprinkle with flour, spreading over surface. Place crust, floured side down, in a 9" pieplate; fold edges under, and flute. Bake at 450° for 5 minutes.
Combine butter, sugar, and corn syrup; cook over low heat, stirring constantly, until sugar dissolves. Let cool slightly. Add chopped pecans and next 3 ingredients; stir well. Pour filling into prebaked piecrust; sprinkle with two-thirds of chopped white chocolate. Top with pecan halves.
Bake at 325° for 50 to 55 minutes or until set. Cover with aluminum foil during last 10 minutes of baking to prevent excessive browning. Let cool on a wire rack.
Place remaining chopped white chocolate in a small heavy-duty, zip-top plastic bag; seal bag. Submerge bag in hot water until chocolate melts. Remove bag from water. Snip a tiny hole in one corner of bag, using scissors; drizzle chocolate over pie.
*For white chocolate, we used Baker's.