Preheat oven to 350°. Line a 13×9-in. baking pan with foil, letting ends extend up sides; grease foil.
Prepare brownie mix batter according to package directions. Transfer to prepared pan. Top with butterscotch chips, coconut and if desired, pecans. Drizzle with milk. Bake until topping is light golden, 35-40 minutes.
Cool completely in pan on a wire rack. Lifting with foil, remove brownies from pan. Cut into bars. Store in an airtight container.