Preheat oven to 350 degrees with the oven rack in the middle. Spray a 9x13" glass baking dish with non-stick spray. Then line with parchment paper that you have cut to fit, 1 sheet going width wise and 1 sheet going length wise. I pin the parchment paper down with metal binder clips. Then spray the parchment paper with non-stick cooking spray.

In a medium size bowl, combine the flour and brown sugar. Whisk to combine. Add in the cold butter, and cut into the flour and sugar with a pastry cutter until the butter is in pea size pieces. Add in the egg and stir to combine. Fold in 1-1/2 cups of the chocolate chips, and all the chopped walnuts. Stir to combine.

Reserve 1-1/2 cups of the flour mixture. Pour the remaining flour mixture into the baking dish. Press in an even layer to the bottom of the baking dish. Bake for 10 minutes.

Remove from oven, and pour in the sweetened condensed milk. Reserve 1/4 cup of the toffee bits. Sprinkle the remaining toffee bits on top of the sweetened condensed milk. Then sprinkle with the reserved 1-1/2 cup flour mixture. Then sprinkle on the remaining 1/2 cup chocolate chips. Bake for another 30 minutes.

Remove from oven. Top with remaining 1/4 cup toffee bits. Allow to cool for 30 minutes. Then lift out of the baking dish with the parchment. Allow to cool completely before cutting into bars.