Preheat oven to 350°F. Line a 13x9-inch pan with parchment paper or foil and grease lightly. In large bowl, combine all crust ingredients; mix at low speed until crumbly but combined.
Reserve half of crumb mixture (about 3 cups) for the topping. Press remaining crumb mixture evenly into the bottom of greased pan. Bake at 350°F. for 10 minutes.
While the crust is baking, stir together the 3 tablespoons flour and caramel sauce.
Remove partially baked crust from oven; sprinkle evenly with chocolate chips and nuts if using. Drizzle evenly with caramel mixture. Sprinkle reserved crumb mixture over the top.
Return to oven. Bake an additional 18 to 22 minutes or until golden brown. Cool for 1 hour or until completely cooled. Refrigerate 1 to 2 hours or until filling is set. Cut into 36 bars.