HEAT oven to 350°F. Grease a 13 x 9-inch pan. Lightly spoon flour into measuring cup; level off. In large bowl, combine all crust ingredients; mix at low speed until crumbly. Reserve half of crumb mixture (about 3 cups) for topping. Press remaining crumb mixture in bottom of greased pan. Bake at 350°F for 10 minutes.
COMBINE caramel topping and 3 tablespoons flour in small bowl; blend well.
REMOVE partially baked crust from oven. Sprinkle with chocolate chips and nuts. Drizzle evenly with caramel mixture. Sprinkle with reserved crumb mixture.
RETURN to oven; bake an additional 18 to 22 minutes or until golden brown. Cool 1 hour or until completely cooled. Refrigerate 1 to 2 hours or until filling is set. Cut into bars.