Combine flour, 1 cup sugar and 1/2 cup butter to make fine crumbs. Press firmly into a greased 9x13 inch pan. Sprinkle with pecans. Cook 1 1/3 cups butter and 1 1/3 cups brown sugar over medium heat, stirring constantly until entire surface boils. Boil for 1 minute and pour over crust. Bake at 350 degrees for 18 to 22 minutes until surface is bubbly. Remove from oven; immediately sprinkle with chocolate chips and swirl.