Preheat oven to 350°F. Prepare Salted Caramel Bar Mix packet 1 according to package directions using 12 tablespoons butter. Reserve ½ cup mix. Press remaining mixture into an 8x8-inch baking dish.
Prepare caramel packet 2 according to package directions using 1½ tablespoons butter and milk. Drizzle half the caramel over bar mixture. Top with chocolate chunks, pecans and remaining bar mixture.
Bake 25 minutes. Remove from oven. Reheat remaining caramel in microwave for 30 seconds; drizzle over bars. Sprinkle with desired amount of salt packet. Let cool 20 minutes. Refrigerate until completely cooled; about 2 hours. Cut into 16 bars.
Makes 16 bars.
Make ahead: Prepare through step 3 up to 2 days ahead. Keep refrigerated.