Preheat oven to 350 degrees F. Line a 13x9x2-inch baking pan with foil, extending foil over pan edges; set aside. In a mixing bowl, beat flour, 1/2 cup brown sugar, and the 1/2 cup butter with an electric mixer on medium speed until mixture resembles fine crumbs. Press mixture evenly into the bottom of the prepared pan.
Bake about 15 minutes or until light brown. Remove from oven. Sprinkle nuts, baking bar, and milk chocolate pieces over hot crust.
In a small saucepan, cook and stir the 3/4 cup butter and the 1/2 cup brown sugar over medium heat until bubbly. Cook and stir for 1 minute more. Pour sugar mixture evenly over bars. Bake about 15 minutes more or just until bubbly around edges. Cool in pan on a wire rack. Using the foil; lift the uncut bars out of the pan. Cut into bars. Layer bars between pieces of waxed paper in tins; cover.