Preheat oven to 350. In a medium bowl, combine flour and sugar, cut in butter until crumbly. Stir in 1/2 cup of chocolate chips.
Press mixture firmly on bottom of 13x9 pan. Bake 15 minutes.
Meanwhile, in a bowl mix sweetened condensed milk, egg, and vanilla; stir in remaining chips and nuts. Spread evenly over prepared crust. Bake 20 to 25 minutes or until golden brown. Cool completely. Cut into bars. Store leftovers at room temperature.