Heat oven to 350° F. In a large bowl, combine butter, flour and brown sugar. With pastry blender or fork, cut in butter until fine crumbs form ( a few large crumbs may remain). Press into ungreased 13 by 9 by 2 inch baking pan. Sprinkle pecans over crust. Prepare Toffee topping; drizzle evenly over pecans and crust. Bake 20 to 22 minutes or until topping is bubbly and golden; remove from oven. Immediately sprinkle milk chocolate chips over top; press gently onto surface. Cool completely in pan on wire rack . Cut into bars. Toffee Topping In small saucepan, combine 2/3 cup butter and 1/3 cup packed light brown sugar; cook over medium heat, stirring constantly, until mixture comes to a boil. Continue boiling, stirring constantly, 30 seconds. Use immediately. Yield: 36 bars