Mix together the flour, brown sugar and butter in a large bowl; stir in the egg.
Stir in the walnuts and 1 1/2 cups of the chocolate chips.
Remove 1 1/2 cups of the flour mixture to a small bowl and set aside.
Press the remaining flour mixture in a greased 9x13 inch baking dish.
Bake at 350 degrees for 10 minutes.
Pour the condensed milk evenly over the crust.
Sprinkle evenly with 1 1/2 cups of the toffee bits.
Sprinkle the 1 1/2 cups flour mixture and the remaining 1/2 cup chocolate chips over the top.
Bake for 25 to 30 minutes or until hot and bubbly and lightly browned.
Sprinkle with the remaining 1/2 cup toffee bits.
Cool completely.
Cut into bars.