Preheat oven to 350°F.
Prepare a 9 x 13-inch pan by lightly buttering the sides.
Combine flour, sugar, and butter pieces in food processor bowl with knife blade attachment; pulse 8-10 times. Particles should resemble coarse crumbs. (To mix by hand, combine dry ingredients then cut butter in with a pastry blender.)
Pour mixture into prepared pan, shake pan to distribute the crumbs evenly. Bake 12 minutes or until lightly browned.
In heavy 2 to 3-quart saucepan, melt butter over medium heat.
Add sugar, corn syrup and sweetened condensed milk. Cook over medium heat stirring constantly. Mixture will caramelize to a golden brown and come to a boil. Continue to cook over medium heat stirring frequently to prevent scorching until the temperature of the mixture reaches 248°F (firm ball stage). Pour mixture evenly onto baked cookie layer in pan.
Sprinkle with chocolate chips, wait 2 minutes; then spread chocolate evenly over candy. Then sprinkle nuts over the warm chocolate.
Allow the candy to thoroughly cool so the chocolate is firm. Cut into approximately 1-inch bars. Store in an airtight container with waxed paper between candy layers.