packed light brown sugar
Heat oven to 350 degrees.
In 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 13x9x2-inch baking pan and sprinkle pecans over crust.
Prepare 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.
Immediately 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 and then cut into bars--about 36 bars.