Preheat oven to 350 degrees. Grease 13x9" baking pan. Combine first 6 ingredients and mix at low speed with mixer until crumbly.Reserve 1/2 (or 3 c) for topping. Press remaining mixture in pan to make a crust. Bake 10 min. Combine caramel topping and 3 tbsp flour nd blend well.Remove crust from oven and sprinkle with chocolate chips and nuts. Drizzle evenly with caramel mixture. Sprinkle with reserved crumbs and return to oven for an additional 18-22 min or until golden brown. Cool and refrigerate 2 hrs until filling is set. Cut into bars.