Preheat oven to 350°F Grease 13X9-mch baking dish.
Whisk flour, salt, baking powder and baking soda in medium bowl. Melt butter in medium saucepan. Remove from heat; stir in brown sugar and granulated sugar with spoon. Add egg and vanilla; stir until well blended. Add flour mixture; mix well. Press into bottom of prepared baking dish; top with apples.
Bake 40 to 45 minutes or until edges are browned and pulling away from sides of pan. Cool completely in pan on wire rack.
Toast pecans in medium nonstick skillet over medium- high heat 2 minutes, stirring constantly, or until fragrant. Remove from skillet; set aside. Wipe out skillet with paper towel. Heat caramels and milk in same skillet over medium-low heat, stirring constantly, until melted and smooth.
Drizzle caramel sauce over cooled apple bars; sprinkle with pecans. Let stand 30 minutes before cutting into bars.