Butter a cookie sheet (11 x 14-inch). Melt butter in heavy 2-quart saucepan, over low heat. Add sugar; heat to boiling, stirring constantly. Stir in water and corn syrup; cook over medium heat, stirring constantly to 290 degrees on candy thermometer; remove from heat. Stir in 1/2 of the nuts. You may want to add 1/2 teaspoons vanilla. Pour candy onto cookie sheet; spread about 1/4-inch thick. Sprinkle chocolate bits over hot candy. As candy melts, spread with spatula, then sprinkle with nuts.