HEAT oven to 350°F. Coat a 13 x 9-inch baking pan with no-stick cooking spray.
STIR together flour and brown sugar in large bowl. Cut in butter with pastry blender or 2 knives until mixture resembles coarse crumbs. Add egg, mixing well. Stir in 1 1/2 cups chocolate chips and nuts. Reserve 1 1/2 cups mixture. Press remaining crumb mixture onto bottom of prepared pan.
BAKE 10 minutes. Pour sweetened condensed milk evenly over partially baked crust. Reserve 1/4 cup toffee bits. Sprinkle remaining toffee bits over layer in pan. Sprinkle reserved crumb mixture and remaining 1/2 cup chocolate chips over top.
BAKE 25 to 30 minutes or until golden brown. Sprinkle with reserved 1/4 cup toffee bits. Cool completely. Cut into bars.